A157538 Half the number of length n integer sequences with sum zero and sum of squares 72.

1, 3, 18, 210, 2565, 32193, 299299, 2161092, 14903940, 101124595, 666560697, 4246100664, 25977358680, 152079371640, 852145833870, 4596664464916, 24033240110143, 122242188808411, 605721155611160, 2925464857935060

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,0,72)/2.

Crossrefs

Sequence in context: A377545 A277355 A135077 * A024488 A217902 A356614

Adjacent sequences: A157535 A157536 A157537 * A157539 A157540 A157541

Keyword

nonn

Author

R. H. Hardin Mar 02 2009

Status

approved