A157550 Half the number of length n integer sequences with sum zero and sum of squares 648.

1, 3, 54, 1830, 68175, 2604105, 72741487, 1575681348, 32584952460, 663445574880, 13119864945495, 250743317040879, 4601891725568592, 80821202263252920, 1358608769903073690, 21985893765384549032, 344851090651019364715

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,0,648)/2.

Crossrefs

Sequence in context: A323325 A224304 A266523 * A224368 A091826 A091796

Adjacent sequences: A157547 A157548 A157549 * A157551 A157552 A157553

Keyword

nonn

Author

R. H. Hardin Mar 02 2009

Status

approved