A157590 - OEIS

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

%S 1,3,186,26130,3296565,312282243,24263695547,1693530847881,

%T 116031418602660,7614709044887230,485263665372726339,

%U 30129597082995141381,1791597506670518058876,101387984322685789268190

%N Half the number of length n integer sequences with sum zero and sum of squares 6728.

%H R. H. Hardin, <a href="/A157590/b157590.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,0,6728)/2.

%K nonn

%O 2,2

%A _R. H. Hardin_ Mar 02 2009