A180805 - OEIS

%I #4 Mar 31 2012 12:35:46

%S 0,4,18,50,136,262,583,974,1794,2603,4560,6190,9987,12617,19419,24264,

%T 35818,41262,61133,70126,97274,110076,154038,167176,230205,247554,

%U 328518,357811,476360,485118,660061,688320,874343,917049,1189870,1192404

%N Number of distinct solutions of sum{i=1..3}(x(2i-1)*x(2i)) = 1 (mod n), with x() in 0..n-1

%C Column 3 of A180813

%H R. H. Hardin, <a href="/A180805/b180805.txt">Table of n, a(n) for n=1..444</a>

%e Solutions for sum of products of 3 0..2 pairs = 1 (mod 3) are

%e (0*0 + 0*0 + 1*1) (0*0 + 0*0 + 2*2) (0*0 + 0*1 + 1*1) (0*0 + 0*1 + 2*2)

%e (0*0 + 0*2 + 1*1) (0*0 + 0*2 + 2*2) (0*0 + 1*2 + 1*2) (0*1 + 0*1 + 1*1)

%e (0*1 + 0*1 + 2*2) (0*1 + 0*2 + 1*1) (0*1 + 0*2 + 2*2) (0*1 + 1*2 + 1*2)

%e (0*2 + 0*2 + 1*1) (0*2 + 0*2 + 2*2) (0*2 + 1*2 + 1*2) (1*1 + 1*1 + 1*2)

%e (1*1 + 1*2 + 2*2) (1*2 + 2*2 + 2*2)

%K nonn

%O 1,2

%A _R. H. Hardin_, suggested by _Max Alekseyev_ in the Sequence Fans Mailing List, Sep 20 2010