A157560 Half the number of length n integer sequences with sum zero and sum of squares 1568.

1, 9, 54, 4730, 384345, 17551611, 639200583, 21540673143, 709364141280, 22449552443395, 690983408959437, 20713553342449344, 594627688939323130, 16245942354519666285, 424430686079103349170, 10684143371864906288080

Offset

2,2

Links

R. H. Hardin, Table of n, a(n) for n=2..50

Formula

[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.

Crossrefs

Sequence in context: A157539 A205814 A157546 * A157588 A270575 A058849

Adjacent sequences: A157557 A157558 A157559 * A157561 A157562 A157563

Keyword

nonn

Author

R. H. Hardin Mar 02 2009

Status

approved