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For questions about sequences of integers. References are often made to the online resource oeis.org.
5
votes
Sequences with integral means
I think I can confirm Noam Elkies' equivalence of sequences (that $r(n)$ is nondecreasing, and that it firsst attains the value $r$ at $n$ equal to the $r$th term in the OEIS sequence A00960)
First w …
29
votes
Accepted
A surprising conjecture about twin primes
Suppose $n-1$ and $n+1$ are both primes.
$\gcd(an+b,bn+a)$ divides $an+b - (bn+a) = (a-b)(n-1)$.
There are two cases. If $n-1$ divides $\gcd(an+b,bn+a)$ then $b=n-1-a$ so $an+b= (n-1) (a+1)$ and $bn …