A157602 - OEIS

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

%S 1,9,378,39990,6207435,649615491,61839617931,5291171373321,

%T 436429418237100,34318546032095787,2635382197485052125,

%U 197482663359487272702,14177933118661639661880,968391907322785974064260

%N Half the number of length n integer sequences with sum zero and sum of squares 9800.

%H R. H. Hardin, <a href="/A157602/b157602.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,0,9800)/2.

%K nonn

%O 2,2

%A _R. H. Hardin_ Mar 02 2009