A011880 a(n) = floor(n*(n-1)/27).

0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 4, 4, 5, 6, 7, 8, 10, 11, 12, 14, 15, 17, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 39, 41, 44, 46, 49, 52, 54, 57, 60, 63, 66, 70, 73, 76, 80, 83, 87, 90, 94, 98, 102, 106, 110, 114, 118, 122, 126, 131, 135, 140, 144, 149, 154, 158, 163, 168, 173

Offset

0,9

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (2, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -2, 1).

Formula

G.f.: x^6(1-x^3+x^5+x^11-x^13+x^16)(1-x^6)/((1-x)(1-x^2)(1-x^3)(1-x^27)).

a(n)= +2*a(n-1) -a(n-2) +a(n-27) -2*a(n-28) +a(n-29). - R. J. Mathar, Aug 11 2021

Maple

A011880:=n->floor(n*(n-1)/27); seq(A011880(n), n=0..100); # Wesley Ivan Hurt, Mar 27 2014

Mathematica

Table[Floor[n*(n - 1)/27], {n, 0, 5!}] (* Vladimir Joseph Stephan Orlovsky, Mar 14 2010 *)
CoefficientList[Series[x^6 (1 - x^3 + x^5 + x^11 - x^13 + x^16) (1 - x^6)/((1 - x) (1 - x^2) (1 - x^3) (1 - x^27)), {x, 0, 70}], x] (* Vincenzo Librandi, Mar 28 2014 *)

Prog

(PARI) a(n)=(n^2-n)\27

Crossrefs

Sequence in context: A097923 A027582 A259198 * A029044 A029043 A296371

Adjacent sequences: A011877 A011878 A011879 * A011881 A011882 A011883

Keyword

nonn,easy

Author

N. J. A. Sloane

Extensions

Typo in Mathematica program fixed by Vincenzo Librandi, Mar 28 2014

Status

approved