A180786 - OEIS

%I #3 Mar 31 2012 12:35:46

%S 0,0,7,30,142,502,1519,3828,9145,18966,38562,70202,127954,211261,

%T 357465,549988,875942,1273587,1941522,2705012,3966472,5325916,7599591,

%U 9892052,13772034,17476435,23770735,29625591,39617904,48129046,63654183,76396024

%N 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 Column 4 of A180793

%H R. H. Hardin, <a href="/A180786/b180786.txt">Table of n, a(n) for n=1..376</a>

%e Solutions for sum of products of 4 1..2 pairs = 1 (mod 3) are

%e (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 (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 (2*2 + 2*2 + 2*2 + 2*2)

%K nonn

%O 1,3

%A _R. H. Hardin_ Sep 20 2010