OFFSET
1,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..10000
S. Ramanujan, Notebook entry.
Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).
FORMULA
G.f.: 6x * (4x^2 + 19x + 4) / (1-x)^4.
Sum_{n>=1} 1/a(n) = (log(3) - 1)/2. - Amiram Eldar, Jul 04 2020
Sum_{n>=1} (-1)^(n+1)/a(n) = 1/2 - 2*log(2)/3. - Amiram Eldar, May 15 2022
MATHEMATICA
Table[27n^3-3n, {n, 40}] (* Harvey P. Dale, Mar 30 2011 *)
PROG
(Magma) [27*n^3-3*n: n in [1..40]]; // Vincenzo Librandi, Sep 07 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Ralf Stephan, Aug 07 2004
STATUS
approved