Voozh

A321004

Number of pairs of primes (i,j) with i<j<n such that i*j == 1 mod n.

0, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 1, 1, 2, 1, 2, 2, 2, 2, 2, 1, 0, 2, 2, 1, 3, 0, 2, 1, 3, 2, 3, 0, 3, 2, 3, 2, 2, 2, 3, 2, 3, 3, 3, 2, 3, 1, 5, 2, 3, 2, 5, 3, 3, 3, 3, 2, 4, 3, 3, 3, 3, 1, 5, 4, 5, 1, 5, 3, 6, 2, 4, 4, 5, 4, 7, 3, 4, 2, 4, 1, 6, 4

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OFFSET

1,16

LINKS

Table of n, a(n) for n=1..85.

MAPLE

with(numtheory);

f:=proc(n) local m, i, j, c; global pi;

if n < 4 then return(0); fi;

c:=0; m:=NumberTheory[pi](n); if isprime(n) then m:=m-1; fi;

for i from 1 to m-1 do p:=ithprime(i);

for j from i+1 to m do