Number of positive divisiors with gcd condition

In summary, There is a general formula to find the number of positive divisors b of n such that (a,b)=1. This formula is similar to the well-known formula for the number of divisors of n, but excludes the primes dividing a.
  • #1
thippli
1
0
Let n be a positive integer and a be a positive divisor of n. Is there any general formula to find the number of positive divisors b of n such that (a,b)=1 ?.
 
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  • #2
No. That would be a formula to factor a number but there isn't any.
 
  • #3
Yes. There is a general formula. First, you should understand the well known formula d(n)=∏(ri+1) for the number of divisors of n, where n=∏piri is the prime factorization of n. See for example wikipedia or OEIS.

In your case, it is the same product as for d(n), except you don't run it over all primes, but exclude the primes dividing a.
 

1. What is the "Number of positive divisors with gcd condition" problem?

The "Number of positive divisors with gcd condition" problem is a mathematical problem that involves finding the number of positive divisors of a given integer that satisfy a specific condition involving the greatest common divisor (gcd) of the divisors.

2. What is the importance of this problem in mathematics?

This problem is important in mathematics because it has applications in various fields such as number theory, combinatorics, and cryptography. It also helps in understanding the structure and properties of integers.

3. How is this problem solved?

This problem can be solved using various techniques such as prime factorization, Euler's totient function, and inclusion-exclusion principle. It also has connections to other mathematical concepts such as Mobius function and Dirichlet convolution.

4. Can you provide an example of solving this problem?

Sure. Let's say we have the integer 12 and we want to find the number of its positive divisors that have a gcd of 6 with 12. The divisors of 12 are 1, 2, 3, 4, 6, and 12. Out of these, only 1 and 6 have a gcd of 6 with 12. Therefore, the answer to this problem would be 2.

5. Are there any real-world applications of this problem?

Yes, this problem has applications in cryptography, particularly in the RSA encryption algorithm. It is also used in analyzing the complexity of algorithms in computer science and in solving problems related to modular arithmetic.

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