A106845 n^2 * (n^3 + 2n^2 + 7n - 2) / 8.

0, 1, 14, 72, 244, 650, 1476, 2989, 5552, 9639, 15850, 24926, 37764, 55432, 79184, 110475, 150976, 202589, 267462, 348004, 446900, 567126, 711964, 885017, 1090224, 1331875, 1614626, 1943514, 2323972, 2761844, 3263400, 3835351, 4484864, 5219577, 6047614, 6977600

Offset

0,3

Comments

a(n) = Sum {1<=k,l,m<=n; k+l+m divisible by n} klm.

Links

Table of n, a(n) for n=0..35.

Index entries for linear recurrences with constant coefficients, signature (6,-15,20,-15,6,-1).

Formula

G.f.: x*(x^4+2*x^3+3*x^2+8*x+1) / (x-1)^6. - Colin Barker, Jul 16 2013

Prog

(PARI) a(n)=if(n<1, 0, sum(k=1, n, sum(l=1, n, sum(m=1, n, if((k+l+m)%n==0, k*l*m))))) /* Michael Somos, May 16 2005 */

Crossrefs

Sequence in context: A074086 A205335 A212750 * A365670 A205328 A328735

Adjacent sequences: A106842 A106843 A106844 * A106846 A106847 A106848

Keyword

nonn,easy

Author

Ralf Stephan, May 06 2005

Extensions

More terms from Colin Barker, Jul 16 2013

Status

approved