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

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
   if ithprime(j)*p mod n =1 then c:=c+1; fi; od: od: c; end;
[seq(f(n), n=1..120)];

Crossrefs

Cf. A320276, A321005.

Sequence in context: A365618 A254885 A108461 * A258595 A233544 A026535

Adjacent sequences: A321001 A321002 A321003 * A321005 A321006 A321007

Keyword

nonn

Author

N. J. A. Sloane, Nov 02 2018

Status

approved