Retractions B

Problem 446

Published on 16 November 2013 at 10:00 pm [Server Time]

For every integer n>1, the family of functions fn,a,b is defined by fn,a,b(x)≡ax+b mod n for a,b,x integer and 0<a<n, 0≤b<n, 0≤x<n.
We will call fn,a,b a retraction if fn,a,b(fn,a,b(x))≡fn,a,b(x) mod n for every 0≤x<n.
Let R(n) be the number of retractions for n.

F(N)=∑R(n4+4) for 1≤n≤N.

Find F(107) (mod 1 000 000 007)

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