A011872 [ n(n-1)/19 ].

0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 4, 5, 6, 8, 9, 11, 12, 14, 16, 18, 20, 22, 24, 26, 29, 31, 34, 36, 39, 42, 45, 48, 52, 55, 59, 62, 66, 70, 74, 78, 82, 86, 90, 95, 99, 104, 108, 113, 118, 123, 128, 134, 139, 145, 150, 156, 162, 168, 174, 180, 186, 192, 199, 205, 212, 218, 225, 232

Offset

0,8

Links

Table of n, a(n) for n=0..67.

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, 1, -2, 1).

Formula

a(n) = +2*a(n-1) -a(n-2) +a(n-19) -2*a(n-20) +a(n-21). [From R. J. Mathar, Apr 15 2010]

G.f.: -((x^5 (1+x^8) (1+(-1+x) x (1+x^2)))/(-1+x (2+x (-1+(-1+x)^2 x^17)))) Peter J. C. Moses, Jun 01 2014

Mathematica

Table[Floor[(n(n-1))/19], {n, 0, 70}] (* or *) LinearRecurrence[ {2, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -2, 1}, {0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 4, 5, 6, 8, 9, 11, 12, 14, 16, 18, 20}, 70] (* Harvey P. Dale, May 25 2013 *)

Crossrefs

Sequence in context: A238886 A060620 A109968 * A056822 A062419 A061052

Adjacent sequences: A011869 A011870 A011871 * A011873 A011874 A011875

Keyword

nonn,easy

Author

N. J. A. Sloane.

Status

approved