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A011871 [ n(n-1)/18 ]. 0
0, 0, 0, 0, 0, 1, 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 13, 15, 17, 19, 21, 23, 25, 28, 30, 33, 36, 39, 42, 45, 48, 51, 55, 58, 62, 66, 70, 74, 78, 82, 86, 91, 95, 100, 105, 110, 115, 120, 125, 130, 136, 141, 147, 153, 159, 165, 171, 177, 183, 190, 196, 203, 210, 217, 224, 231, 238 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,8

LINKS

Table of n, a(n) for n=0..66.

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

FORMULA

a(n) = +2*a(n-1) -a(n-2) +a(n-9) -2*a(n-10) +a(n-11). G.f.: x^5*(x^2-x+1) / ( (1-x)^3*(1+x+x^2)*(x^6+x^3+1) ). - R. J. Mathar, Apr 15 2010

a(n) = floor( (1/3) * sum_{i=1..n} floor(i/3) ). - Wesley Ivan Hurt, Jun 06 2014

MATHEMATICA

Table[Floor[n (n-1)/18], {n, 0, 70}] (* or *) LinearRecurrence[{2, -1, 0, 0, 0, 0, 0, 0, 1, -2, 1}, {0, 0, 0, 0, 0, 1, 1, 2, 3, 4, 5}, 71] (* Harvey P. Dale, Apr 25 2012 *)

CROSSREFS

Sequence in context: A132018 A334142 A044919 * A229769 A130676 A039227

Adjacent sequences:  A011868 A011869 A011870 * A011872 A011873 A011874

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Dec 11 1996

STATUS

approved

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Last modified May 14 04:12 EDT 2021. Contains 343872 sequences. (Running on oeis4.)