Obtaining the number of factors from prime factorization

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Discussion Overview

The discussion revolves around determining the number of distinct factors of the number 2520 based on its prime factorization. Participants explore different methods and interpretations related to combinations of prime factors and the divisor function in number theory.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant claims that the prime factorization of 2520 is 2*2*2*3*3*5*7 and calculates the number of combinations of these factors as C(8,1)+C(8,2)+...+C(8,8)=155, but acknowledges that these are not distinct.
  • Another participant challenges the first claim, stating that 2520 has 4 distinct prime factors, not "8 different primes," and questions the relevance of combinations in this context.
  • A third participant suggests that combinations of prime factors relate to all factors, providing examples of products formed from selected primes.
  • A later reply reiterates the initial claim about the prime factorization and introduces the divisor function, stating that the number of factors can be calculated as (1+n1)(1+n2)(1+n3)... for the respective powers of the prime factors, concluding that 2520 has 48 factors.

Areas of Agreement / Disagreement

Participants express disagreement regarding the interpretation of the number of distinct factors and the relevance of combinations of prime factors. There is no consensus on the correct method to determine the number of factors.

Contextual Notes

Participants have not resolved the assumptions regarding the definitions of distinct factors versus combinations, leading to different interpretations of the problem. The discussion includes unresolved mathematical steps related to the divisor function.

danne89
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Hi! How do I determine the number of distinct factors of a number, say, 2520?
2520 = 2*2*2*3*3*5*7
So we've 8 different primes. The number of combinations of those is, according to me:
C(8,1)+C(8,2)+...+C(8,8)=155 (I think, calculated it by hand; but it isn't important)
Obviously those aren't distinct. (Pick the fist 2 and the second 2 = 4, but pick the second 2 and the third 2 also = 4.)
 
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I don't understand what you are doing. 2520= 2*2*2*3*3*5*7 has 4 distinct prime factors, not "8 different primes". And I don't see what being "prime factors" has to do with number of combinations. Are you asking "of those 8 numbers (not all distinct) how many combinations can I make"? Wouldn't that be the same as asking "of the 8 letters "aaabbcd", how many different combinations can I make?" There are only 3 different one letter combinations: "a", "b", and "c", not C(8,1)= 8.
 
Isn't the combinations of the prime factors = all factors?
I mean, i pick 2*2 (a product of the primes in the positions specified by the combination) or 12
i pick 2*2 or 23
i pick 2*3 or 24

and so on.
Do you see?
 
danne89 said:
Hi! How do I determine the number of distinct factors of a number, say, 2520?
2520 = 2*2*2*3*3*5*7
So we've 8 different primes. The number of combinations of those is, according to me:
C(8,1)+C(8,2)+...+C(8,8)=155 (I think, calculated it by hand; but it isn't important)
Obviously those aren't distinct. (Pick the fist 2 and the second 2 = 4, but pick the second 2 and the third 2 also = 4.)
This is a special case of the divisor functions studied in number theory where you sum the kth power of the divisors.
In this case the 0th power.
say your number factors as
p1^n1*p2^n2*p3^n3*...*pk^nk*...
a general factor (including improper ones) is
p1^m1*p2^m2*p3^m3*...*pk^mk*...
where pk is a prime and 0<=mk<=nk
Thus the number of such factors is
(1+n1)(1+n2)(1+n3)...(1+nk)...
In particular 1 has one factor and and p^n (p prime) has n+1
2520 has 4*3*2*2=48
see this link for more info
http://mathworld.wolfram.com/DivisorFunction.html
 

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