OFFSET
0,2
COMMENTS
a(n) is a perfect cube.
LINKS
Indranil Ghosh, Table of n, a(n) for n = 0..100
Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).
FORMULA
a(n) = A003215(n-1)^3.
a(n) = (3*n^2 - 3*n + 1)^3.
G.f.: (1 + 336*x + 4479*x^2 + 9808*x^3 + 4479*x^4 + 336*x^5 + x^6) / (1 - x)^7. - Colin Barker, Jan 02 2017
PROG
(Python)
def a(n):
return 27*n**6-81*n**5+108*n**4-81*n**3+36*n**2-9*n+1
(PARI) Vec((1 + 336*x + 4479*x^2 + 9808*x^3 + 4479*x^4 + 336*x^5 + x^6) / (1 - x)^7 + O(x^30)) \\ Colin Barker, Jan 02 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Indranil Ghosh, Jan 02 2017
STATUS
approved