A180807 - OEIS

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

%S 0,9,84,474,2325,8468,28778,79670,212049,484180,1100299,2210931,

%T 4457004,8097649,15007266,25353330,43846972,69637926,114422914,

%U 173562451,272208103,396802048,601571401,847452462,1246173200,1706973960

%N Number of distinct solutions of sum{i=1..5}(x(2i-1)*x(2i)) = 1 (mod n), with x() in 0..n-1

%C Column 5 of A180813

%H R. H. Hardin, <a href="/A180807/b180807.txt">Table of n, a(n) for n=1..250</a>

%e Solutions for sum of products of 5 0..1 pairs = 1 (mod 2) are

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

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

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

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

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

%K nonn

%O 1,2

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