cp's OEIS Frontend

A180786 Number of distinct solutions of sum{i=1..4}(x(2i-1)*x(2i)) = 1 (mod n), with x() only in 1..n-1.

%I A180786 #5 Jun 02 2025 03:05:27
%S A180786 0,0,7,30,142,502,1519,3828,9145,18966,38562,70202,127954,211261,
%T A180786 357465,549988,875942,1273587,1941522,2705012,3966472,5325916,7599591,
%U A180786 9892052,13772034,17476435,23770735,29625591,39617904,48129046,63654183,76396024
%N A180786 Number of distinct solutions of sum{i=1..4}(x(2i-1)*x(2i)) = 1 (mod n), with x() only in 1..n-1.
%C A180786 Column 4 of A180793
%H A180786 R. H. Hardin, <a href="/A180786/b180786.txt">Table of n, a(n) for n=1..376</a>
%e A180786 Solutions for sum of products of 4 1..2 pairs = 1 (mod 3) are
%e A180786 (1*1 + 1*1 + 1*1 + 1*1) (1*1 + 1*1 + 1*1 + 2*2) (1*1 + 1*1 + 2*2 + 2*2)
%e A180786 (1*1 + 1*2 + 1*2 + 1*2) (1*1 + 2*2 + 2*2 + 2*2) (1*2 + 1*2 + 1*2 + 2*2)
%e A180786 (2*2 + 2*2 + 2*2 + 2*2)
%K A180786 nonn
%O A180786 1,3
%A A180786 _R. H. Hardin_ Sep 20 2010