A001447 a(n) = (5^n + 5^floor(n/2))/2.

1, 3, 15, 65, 325, 1575, 7875, 39125, 195625, 976875, 4884375, 24415625, 122078125, 610359375, 3051796875, 15258828125, 76294140625, 381469921875, 1907349609375, 9536744140625, 47683720703125

Offset

0,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..300

Index entries for linear recurrences with constant coefficients, signature (5,5,-25).

Formula

a(n) = 5*a(n-1) + 5*a(n-2) - 25*a(n-3); a(0)=1, a(1)=3, a(2)=15. - Harvey P. Dale, May 05 2011

G.f.: (1 - 2x - 5x^2)/(1 - 5x - 5x^2 + 25x^3). - Harvey P. Dale, May 05 2011

Mathematica

Table[(5^n+5^Floor[n/2])/2, {n, 0, 20}] (* or *) LinearRecurrence[ {5, 5, -25}, {1, 3, 15}, 50](* Harvey P. Dale, May 05 2011 *)

Prog

(PARI) a(n)=(5^n+5^(n\2))/2 \\ Charles R Greathouse IV, Apr 17 2012

Crossrefs

Sequence in context: A080948 A098102 A144067 * A106732 A052981 A086200

Adjacent sequences: A001444 A001445 A001446 * A001448 A001449 A001450

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved