A157538 - OEIS

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

%S 1,3,18,210,2565,32193,299299,2161092,14903940,101124595,666560697,

%T 4246100664,25977358680,152079371640,852145833870,4596664464916,

%U 24033240110143,122242188808411,605721155611160,2925464857935060

%N Half the number of length n integer sequences with sum zero and sum of squares 72.

%H R. H. Hardin, <a href="/A157538/b157538.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,0,72)/2.

%K nonn

%O 2,2

%A _R. H. Hardin_ Mar 02 2009