A157564 - OEIS

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

%S 1,3,6,6830,561735,29360121,1242596383,47858305311,1805644314360,

%T 65361758855305,2298374956416891,78740814179665443,

%U 2583344854373884146,80658838456091971635,2408249945284962451650,69283128843699421305698

%N Half the number of length n integer sequences with sum zero and sum of squares 2048.

%H R. H. Hardin, <a href="/A157564/b157564.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,0,2048)/2.

%K nonn

%O 2,2

%A _R. H. Hardin_ Mar 02 2009