
#37
Dec2407, 10:27 PM

P: 258





#38
Dec2507, 06:28 AM

P: 688

Post #9 shows examples of primes not of the form p + 2^n. I imagine that finding counterexamples for p  2^n (in particular, checking those on A065381) is harder, since there is no limit to p or 2^n.




#39
Dec2507, 10:45 AM

P: 258

Consider the two sets: S = set of primes of the form p + 2^n S' = set of primes of the form p  2^n If we prove that all primes should be in one of these two sets the infinity of the two sets will be proved. In fact post #5 shows that the primes not in S may could be found in the infinity of the negative integer line as p + 2^n, which I wonder is the same thing of find this primes in the infinity of the positive integer line as p  2^n. We can search to infinity for them, increasing both p and 2^n until find a match. This is why [tex]S \subset\ S'[/tex], I think. This is why trying to show that primes are in the form p + 2^n contain "gaps" = p  2^n. And now, by Tchebychef: for m > 1 there is at least one prime p such that m < p < 2m if we put m = 2^n, n a natural > 0 ==> 2^n < p < 2^(n+1) perhaps this theorem could be usefull 



#40
Dec2607, 06:04 PM

P: 258

Let all positive whole number be written as a sum of power of two:
[tex]1 = 2^0[/tex] [tex] 2 = 2^1[/tex] [tex] 3 = 2^0 + 2^1[/tex] [tex] 4 = 2^2[/tex] [tex] 5 = 2^0 + 2^2[/tex] [tex] 6 = 2^1 + 2^2 [/tex] [tex] 7 = 2^0 + 2^1 + 2^2[/tex] [tex] 8 = 2^3 [/tex] [tex] 9 = 2^0 + 2^3[/tex] [tex] 10 = 2^1 + 2^3[/tex] [tex] 11 = 2^0 + 2^1 + 2^3[/tex] [tex] 12 = 2^2 + 2^3[/tex] [tex] 13 = 2^0 + 2^2 + 2^3[/tex] [tex] 14 = 2^1 + 2^2 + 2^3[/tex] [tex] 15 = 2^0 + 2^1 + 2^2 + 2^3[/tex] [tex] 16 = 2^4 [/tex] [tex] 17 = 2^0 + 2^4[/tex] [tex] 18 = 2^1 + 2^4[/tex] [tex] 19 = 2^0 + 2^1 + 2^4[/tex] [tex] 20 = 2^2 + 2^4 etc...[/tex] We know by Tchebychef: for m > 1 there is at least one prime p such that m < p < 2m if we put m = 2^n, n a natural > 0 ==> 2^n < p < 2^(n+1) We know by Gauss: the number of primes from 1 to x is approximately =[tex]\frac{x}{ln(x)}[/tex] The number of primes between [tex] 2^n[/tex] and [tex] 2^{n+1}[/tex] is approximately = [tex]\frac{2^{n+1}}{ln(2^{n+1})}  \frac{2^n}{ln(2^n)}[/tex] = [tex]\frac{2^n}{ln(2)}*(\frac{2}{n+1}  \frac{1}{n})[/tex] = [tex]\frac{2^n}{ln(2)}*(\frac{n1}{n^2+n})[/tex] and we know that [tex]2^n > n^2[/tex] for [tex]\geq 3[/tex] ==> [tex]\frac{2^n}{ln(2)}*(\frac{n1}{n^2+n})[/tex] diverges for n > [tex]\infty[/tex] for n increasing the Tchebychef's theorem underestimates the amount of primes 



#41
Dec2707, 08:32 AM

Sci Advisor
HW Helper
P: 3,680

I'm not sure why you're measuring the primes between [itex]2^n[/itex] and [itex]2^{n+1}[/itex]. The relevant probabilities are
[tex]1/\ln(p+2)[/tex] [tex]1/\ln(p+4)[/tex] [tex]1/\ln(p+8)[/tex] . . . Thus the relevant question is: Does [tex](11/\ln(p+2))(11/\ln(p+4))\cdots[/tex] diverge to 0? Ignoring p, this is [tex](1k)(1k/2)(1k/3)\cdots[/tex] for [tex]k=1/\ln2[/tex]. [tex]\prod_n(1k/n)=\exp\sum_n\ln(1k/n)=\exp\left(\sum_n k/n+k^2/2n^2+\cdots\right)\ge\exp\left(\sum_n k/n\right)=e^{\infty}=0[/tex] so the product is 0 and so we do expect that all odds are of the form [itex]p2^n[/itex] for prime p and some positive n. 



#42
Dec2707, 12:45 PM

P: 258

This is the point: seems to me that you already are considering that there are such primes of the form [tex]p + 2^n[/tex], and we don't know yet. Or did I not understand some particular point?
My idea on measuring the primes between [itex]2^n[/itex] and [itex]2^{n+1}[/itex]: Lets discriminate the numbers in classes according to the highest exponent, such that the nthclass has [itex]2^n[/itex] numbers, etc. Considering some prime number in nthclass like [itex]2^0 + 2^a + 2^b + 2^n[/itex], we should have [itex]2^0 + 2^b + 2^n[/itex], [itex]2^0 + 2^a + 2^n[/itex] or [itex]2^0 + 2^a + 2^b[/itex] = prime, or if for some reason this particular prime couldn't be written of the form [itex]p + 2^n[/itex], we should have [itex]2^0 + 2^a + 2^b + 2^n + 2^k[/itex] a prime number for some [itex]2^k[/itex] exponent, writting this prime in the [itex]p  2^n[/itex] form. My idea: [tex]\frac{2^n}{ln(2)}*(\frac{n1}{n^2+n})[/tex] should give us the number of primes expected in the nthclass, and then we'll be able do find the probability that some particular prime number have a permutation of the exponents that represents another prime number. By doing these calculations I hope that the probability increases when n increases. Honestly I don't feel that these statistical procedures could give us an absolute proof, only heuristics evidences. 



#43
Dec2707, 12:58 PM

P: 258

* because obviously [tex]2^0 + 2^a + 2^b + 2^n + 2^k  2^k[/tex] is the same prime, so we can keep adding exponents until find some k such that [tex]2^0 + 2^a + 2^b + 2^n + 2^k[/tex] represents a prime; and as we know that for every prime of the form [tex]p  2^n[/tex] there is a prime of the form [tex]p + 2^n[/tex], this should give us our proof.
ps: I had to write this sentence here because TEX become crazy and change the expressions 



#44
Dec2907, 06:04 AM

Sci Advisor
HW Helper
P: 4,301

{491,{8,7,6,5,3}} should be read as [tex]491  3 = 2^8 + 2^7 + 2^6 + 2^5 + 2^3[/tex]. In the attachment I have plotted the occurring powers for the first 1000 primes (except 2 and 3). Have fun PS the Mathematica code, in case anyone wants to reproduce this




#45
Dec2907, 10:51 AM

P: 258

1. using numbers like [tex]p+3, p+5, p+9, p+17,..., p+2^n+1[/tex], or [tex]p+1, p+3, p+7, p+15,..., p+2^n1[/tex] to calculate the convergence to zero, seems to return almost the same result, so I think that this approach may not work 2. this seems to work only with p fixed, so we cannot search for [tex]p  2^n[/tex] because we cannot calc the log of negative numbers (in case of to exclude a fixed p), and specially because we should increase p when n increases, so p cannot be a fixed constant such that it can be excluded 3. to exclude p should give us the same result of calculate the probabilities of [tex] 2, 2^2, 2^3, ..., 2^n, ... [/tex] be prime numbers, when only 2 is a prime number ==> both results cannot be the same 



#46
Dec2907, 11:13 AM

Sci Advisor
HW Helper
P: 3,680

http://www.dartmouth.edu/~chance/cha...ann/cramer.pdf The magnitude of the number is the only thing that matters for the GaussTchebychev expectation 1/log(x). Obviously if you know about the divisibility of the number by small primes that will tell you more  in fact this can be stated explicitly in what I call the CramerMaier model of the primes  but that's only changing a multiplicative constant; the magnitude remains only the exponential part 2^k. 



#47
Jan208, 10:18 PM

P: 258

I was thinking about this approach (I don't know the difference between odds, chances and probability in english, so I used the word probability) :
The expression Q = [tex]\frac{2^n}{ln(2)}*(\frac{n1}{n^2+n})[/tex] give us an estimate of the amount of primes between [tex]2^{n+1} and \ 2^n[/tex] The formula [tex]\frac{\frac{2^n}{ln(2)}*(\frac{n1}{n^2+n})}{2^{n+1}  2^n} = \frac{\frac{2^n}{ln(2)}*(\frac{n1}{n^2+n})}{2^n*(2  1)} = \frac{1}{ln(2)}*(\frac{n1}{n^2+n})[/tex] should give us the probability of a particular sum of powers of two (inside the " nthclass [tex]2^n[/tex] " whose amount of numbers is obviously = [tex]2^n[/tex] ) represent a prime. The formula [tex]\frac{1}{2^n}[/tex] should give us the probability of a particular number be this particular sum of powers of two + some power of two, because every number has a unique sum of powers of two representation. The probability of both events is = [tex]\frac{\frac{1}{ln(2)}*(\frac{n1}{n^2+n})}{2^n}[/tex] Let this particular sum be = q, so we ask if there are infinite prime numbers p such that [tex] p = q + 2^n[/tex]. The questions are: 1) what is the probability of the same prime represent another primes taking increasing exponents, for example: [tex]p_1 = q + 2^{n_1}, p_2 = q + 2^{n_2}, p_3 = q + 2^{n_3}, ..., p_k = q + 2^{n_k}[/tex]; or 2) what is the probability of "there are infinite classes with at least one prime of the form [tex] p = q + 2^n [/tex] inside the class"?[tex]/[/tex] The first questions I think may be answered by the product: [tex]\prod^{n}_{k=2} \frac{\frac{1}{ln(2)}*(\frac{k1}{k^2+k})}{2^k}[/tex] = [tex]\prod^{n}_{k=2} \frac{\frac{1}{ln(2)}*(\frac{k1}{k*(k+1)})}{2^k}^{[1]}[/tex] This product converges to zero because it represents the probability of each of the existing classes as having at least a prime number such like that ([tex]p_k = q + 2^{n_k}[/tex] with q fixed), and I think that this is because the fixed "q". But this is not the "right question to ask" since this result cannot be interpreted as a proof of the "non infinity" (I don't know if exists such word in english...) of the set of [tex]p_1 = q + 2^{n_1}; p_2 = q + 2^{n_2}; p_3 = q + 2^{n_3}; ...; p_k = q + 2^{n_k}[/tex], because even if there is not a prime such that [tex]p_k = q + 2^{n_k}[/tex] in each of the existing classes we still could have infinite number primes of that form in another classes (like only in odd classes, etc). Then I think that perhaps could be more prolific to work with the more general question: " to calculate the probability of an any prime of the nthclass, considering all primes into this class, be combined with an exponent 2^n such that will be equal to a prime of the (n1)thclass OR the probability of an any prime of the (n1)thclass, considering all primes into this class, be combined with an exponent +2^n such that will be equal to a prime of the (n1)thclass OR the probability of an any prime of the nthclass, considering all primes into this class, be combined with an exponent 2^m (m<n) such that will be equal to a prime of the same nthclass OR the probability of an any prime of the nthclass, considering all primes into this class, be combined with an exponent +2^m (m<n) such that will be equal to a prime of the same nthclass" This should increase our chances, because the probabilities will be added. But supose that we find a result that diverge to infinite, or that is convergent to a value > 1, in this cases how to interpret such results in terms of probabilities? [1] k=1 doesn't matter because [tex]2^1[/tex] is the first class such that among the elements there is a prime (in fact, the only element is a prime) 



#48
Jan308, 09:45 AM

Sci Advisor
HW Helper
P: 3,680

[tex]\frac{n1}{n(n+1)\log2}\approx\frac{1}{n\log2}[/tex], the probability of being prime, for the chosen number. If you mean "p = q + 2^n, where p and q are prime" then we're back to your original question. [tex]\sum_{k=1}^\infty\frac{1}{(2^k + q)\log(2^k+q)}\approx C+\sum_{k=2}^\infty\frac{1}{k\cdot2^k}[/tex] for some (small) constant C. But if you accept that each such class (for given prime q) is finite, then the problem simplifies to "are there infinitely many primes q such that q+2^k is prime for some integer k?". 



#49
Jan308, 09:50 AM

Sci Advisor
HW Helper
P: 3,680

A094076 seems to strongly suggest that such an infinite set exists. 



#50
Jan308, 07:14 PM

P: 258

Perhaps the fact [tex]2^{n+1}  2^n = 2^n[/tex] could be usefull to infer adjacent classes relations, or even not adjacent classes relations. Then in the nthclass what is the probability of [tex]x = 2^0 + 2^2 + 2^n[/tex] be a prime number? The probability of x be prime "times" the probability of [tex]2^0 + 2^2 = 5[/tex] be combined with an exponent [tex]2^n[/tex]. But you are right, this last probability is wrong. My mistake was the second probability calculation, let me try to make myself clear and correct the mistake: Lets take a look on: [tex]1 = 2^0[/tex] [tex] 2 = 2^1[/tex] [tex] 3 = 2^0 + 2^1[/tex] [tex] 4 = 2^2[/tex] [tex] 5 = 2^0 + 2^2[/tex] [tex] 6 = 2^1 + 2^2 [/tex] [tex] 7 = 2^0 + 2^1 + 2^2[/tex] [tex] 8 = 2^3 [/tex] [tex] 9 = 2^0 + 2^3[/tex] [tex] 10 = 2^1 + 2^3[/tex] [tex] 11 = 2^0 + 2^1 + 2^3[/tex] [tex] 12 = 2^2 + 2^3[/tex] [tex] 13 = 2^0 + 2^2 + 2^3[/tex] [tex] 14 = 2^1 + 2^2 + 2^3[/tex] [tex] 15 = 2^0 + 2^1 + 2^2 + 2^3[/tex] [tex] 16 = 2^4 [/tex] [tex] 17 = 2^0 + 2^4[/tex] [tex] 18 = 2^1 + 2^4[/tex] [tex] 19 = 2^0 + 2^1 + 2^4[/tex] [tex] 20 = 2^2 + 2^4 etc...[/tex] This should let us conclude, without any formal proof, that all the elements of a "class" (considering a "class" the set of all elements with the same highest exponent) are a sum of the highest exponent of the class and each of the elements of all the precedents "classes" (but not the first element 2^n itself[tex]^{[1]}[/tex]). For example, 3thclass (exponent 2^3): [1] this is because [itex]1+2^1+2^2+...+2^n=2^{n+1}1[/itex],i.e, the total of the precedent exponents (which I call "classes") is the the total of elements of the following class minus one [tex]8 = 2^3 [/tex] the first element is the exception [tex]9 = 2^0 + 2^3[/tex] where [tex]2^0[/tex] is an element of the zeroclass [tex]10 = 2^1 + 2^3[/tex] where [tex]2^1[/tex] is an element of the first class [tex]11 = 2^0 + 2^1 + 2^3[/tex] where [tex]2^0+2^1[/tex] is an element of the first class [tex]12 = 2^2 + 2^3[/tex] where [tex]2^2[/tex] is an element of the second class [tex]13 = 2^0 + 2^2 + 2^3[/tex] where [tex]2^0+2^2[/tex] is an element of the second class [tex]14 = 2^1 + 2^2 + 2^3[/tex] where [tex]2^2+2^3[/tex] is an element of the second class [tex]15 = 2^0 + 2^1 + 2^2 + 2^3[/tex] where [tex]2^1+2^2+2^3[/tex] is an element of the second class This lead us to ask for the probability of an arrangement of 2exponents of a prime in the last class, already taking off the greater 2exponent, be exacly a prime of one of the precedent classes. More generally, we could ask for the probability of an arrangement of 2exponents of a prime in the last class be exacly a prime of one of the precedent classes, tanking off ONE of the any 2exponents (but not 2^0 obviously). This should consider an arrangement inside the class itself. And of course we can extend this to the primes of the form p  2^n. Hope I make myself clear now, please consider the english barrier. 



#51
Jan308, 07:22 PM

P: 258

We know that [tex]\frac{1}{2} + \frac{1}{4} + \frac{1}{8} + ... \ =1[/tex], but your sum above seems to converges to 0.16667 or something like that




#52
Jan308, 09:18 PM

Sci Advisor
HW Helper
P: 3,680

What you call a kclass I call a (k+1)bit number. So you're asking for the probability that a (k+1)bit number, less its most significant bit (2^k), is prime "of one of the precedent classes". The precedent classes would then be those numbers below 2^k. But since the number minus 2^k is always under 2^k, this is just the probability that a (k+1)bit number, less its most significant bit, is prime. Alright, I can see how that is relevant. This is the power of two that leaves the smallest remainder when subtracted from the original, making the remaining number most likely to be prime. 



#53
Jan308, 09:22 PM

Sci Advisor
HW Helper
P: 3,680

If I make enough progress on it I'll send Sloane the updates and post them here as well. 



#54
Jan608, 09:51 AM

P: 258

I'll make a comment about another observation of mine that involves twin prime conjecture. In order to find an appropriate heuristic argument could be more prolific if we work in the same particular direction, because there are a lot of possibilities. 


Register to reply 
Related Discussions  
Cells are made of molecules,molecules are made of atoms,atoms are made of energy.so..  Biology  9  
BKL Conjecture  Special & General Relativity  0  
Name that conjecture  General Math  4  
Proof of Golbach's conjecture and the twin prime conjecture  Linear & Abstract Algebra  9  
My Conjecture  General Discussion  0 