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

%S 1,3,126,2170,37335,921333,21967484,466292604,9161931075,164162481681,

%T 2705726857350,41747317681290,619096670144225,8923605271290360,

%U 124998845674120920,1699006653803990456,22382667992161145863

%N Half the number of length n integer sequences with sum zero and sum of squares 450.

%H R. H. Hardin, <a href="/A157547/b157547.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,0,450)/2.

%K nonn

%O 2,2

%A _R. H. Hardin_ Mar 02 2009