A011883 a(n) = floor(n*(n-1)/30).

0, 0, 0, 0, 0, 0, 1, 1, 1, 2, 3, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 42, 44, 46, 49, 52, 54, 57, 60, 63, 66, 69, 72, 75, 78, 81, 85, 88, 91, 95, 99, 102, 106, 110, 114, 118, 122, 126, 130, 134, 138, 143, 147, 151, 156, 161, 165

Offset

0,10

Links

Harvey P. Dale, Table of n, a(n) for n = 0..1000

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

Formula

From R. J. Mathar, Apr 15 2010: (Start)

a(n) = 2*a(n-1) - a(n-2) + a(n-15) - 2*a(n-16) + a(n-17).

G.f.: x^6*(x^2 - x + 1)*(x^4 - x^2 + 1)/((1 - x)^3*(1 + x^4 + x^3 + x^2 + x)*(1 + x + x^2)*(1 - x + x^3 - x^4 + x^5 - x^7 + x^8)). (End)

Mathematica

Join[{0}, Floor[#/15]&/@Accumulate[Range[0, 80]]] (* or *) Table[Floor[ (n(n-1))/30], {n, 0, 80}] (* Harvey P. Dale, May 18 2019 *)

Prog

(Magma) [(n*(n-1)) div 30: n in [0..100]]; // Vincenzo Librandi, May 19 2019
(PARI) a(n) = (n*(n-1))\30; \\ Michel Marcus, May 19 2019

Crossrefs

Sequence in context: A101788 A348776 A024698 * A034886 A011882 A025767

Adjacent sequences: A011880 A011881 A011882 * A011884 A011885 A011886

Keyword

nonn,easy

Author

N. J. A. Sloane

Extensions

More terms from Vladimir Joseph Stephan Orlovsky, Mar 14 2010

Status

approved