%I A157560
%S A157560 1,9,54,4730,384345,17551611,639200583,21540673143,709364141280,
%T A157560 22449552443395,690983408959437,20713553342449344,594627688939323130,
%U A157560 16245942354519666285,424430686079103349170,10684143371864906288080
%N A157560 Half the number of length n integer sequences with sum zero and sum of 
               squares 1568.
%H A157560 Ron Hardin, <a href="b157560.txt">Table of n, a(n) for n=2..50</a>
%F A157560 [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,0,1568)/2.
%Y A157560 Sequence in context: A093847 A157539 A157546 this_sequence A157588 A058849 
               A058852
%Y A157560 Adjacent sequences: A157557 A157558 A157559 this_sequence A157561 A157562 
               A157563
%K A157560 nonn
%O A157560 2,2
%A A157560 Ron Hardin (rhhardin(AT)att.net) Mar 02 2009