A011877 a(n) = floor(n*(n-1)/24).

0, 0, 0, 0, 0, 0, 1, 1, 2, 3, 3, 4, 5, 6, 7, 8, 10, 11, 12, 14, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 36, 38, 41, 44, 46, 49, 52, 55, 58, 61, 65, 68, 71, 75, 78, 82, 86, 90, 94, 98, 102, 106, 110, 114, 119, 123, 128, 133, 137, 142, 147, 152, 157, 162, 168, 173, 178, 184, 189

Offset

0,9

Links

Table of n, a(n) for n=0..68.

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

Formula

a(n) = +2*a(n-1) -a(n-2) +a(n-3) -2*a(n-4) +a(n-5) -a(n-6) +2*a(n-7) -a(n-8) +a(n-9) -2*a(n-10) +a(n-11) -a(n-12) +2*a(n-13) -a(n-14) +a(n-15) -2*a(n-16) +a(n-17) -a(n-18) +2*a(n-19) -a(n-20) +a(n-21) -2*a(n-22) +a(n-23). G.f.: x^6*(1-x+x^2-x^3+x^6-x^9+x^10-x^11+x^12) / ((1-x)^3*(1+x+x^2)*(x^2+1)*(x^4+1)*(x^4-x^2+1)*(x^8-x^4+1) ). [From R. J. Mathar, Apr 15 2010]

Mathematica

CoefficientList[Series[x^6*(1-x+x^2-x^3+x^6-x^9+x^10-x^11+x^12) / ((1-x)^3 *
(1+x+x^2) * (x^2+1) * (x^4+1) * (x^4-x^2+1) * (x^8-x^4+1)), {x, 0, 200}], x] (* Georg Fischer, Sep 28 2022 *)

Crossrefs

Sequence in context: A091848 A017886 A029038 * A029064 A029037 A017875

Adjacent sequences: A011874 A011875 A011876 * A011878 A011879 A011880

Keyword

nonn,easy

Author

N. J. A. Sloane.

Status

approved