OFFSET
0,2
COMMENTS
Always an integer. Can be expressed as a polynomial with rational coefficients of degree 5.
LINKS
Index entries for linear recurrences with constant coefficients, signature (6,-15,20,-15,6,-1).
FORMULA
a(n) = n/120 * (96n^4 + 765n^3 + 2210n^2 + 2275n + 1354).
G.f.: x*(x^4-5*x^3+10*x^2+30*x+60) / (x-1)^6. - Colin Barker, Jun 15 2013
PROG
(PARI) a(n)=60*sum(k=1, n, sum(j=1, k, sum(i=1, j, i^2*j/k)))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Benoit Cloitre, Oct 25 2003
STATUS
approved