A157593 - OEIS

%I #4 Mar 31 2012 12:35:25

%S 1,9,378,37830,3403815,290684541,23648592268,2009304033948,

%T 165069279069345,12108533607540535,813240975212887518,

%U 51447280837022648370,3118521194576489150631,182797738828031587273965

%N Half the number of length n integer sequences with sum zero and sum of squares 7442.

%H R. H. Hardin, <a href="/A157593/b157593.txt">Table of n, a(n) for n=2..50</a>

%F [cache enabling] count(n,s,ss)->count(n,t,tt) where t=s mod n, q=(t-s)/n, tt=ss+2*q*s+n*q^2; count(n,t,tt)=sum[i^2<=tt]{ count(n-1,t-i,tt-i^2) }. a(n)=count(n,0,7442)/2.

%K nonn

%O 2,2

%A _R. H. Hardin_ Mar 02 2009