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A005030 a(n) = 5*3^n. 6
5, 15, 45, 135, 405, 1215, 3645, 10935, 32805, 98415, 295245, 885735, 2657205, 7971615, 23914845, 71744535, 215233605, 645700815, 1937102445, 5811307335, 17433922005, 52301766015, 156905298045, 470715894135, 1412147682405, 4236443047215, 12709329141645 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Limit of sigma(a(n))/a(n), when n tends to infinity is 9/5 = sigma(10)/10 (see Ward link). - Michel Marcus, Apr 30 2013

LINKS

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

Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets

Tanya Khovanova, Recursive Sequences

Jeffrey Ward, Does Ten Have a Friend?, arXiv:0806.1001 [math.NT], 2008.

Index entries for linear recurrences with constant coefficients, signature (3).

FORMULA

O.g.f.: 5/(1-3*x). - R. J. Mathar, Jan 31 2008

G.f.: 1/x + 2 - 2/x/G(0), where G(k)= 1 + 1/(1 - x*(5*k-3)/(x*(5*k+2) - 1/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, Jun 04 2013

a(n) = 5*A000244(n). - Michel Marcus, Aug 25 2016

MATHEMATICA

5*3^Range[0, 60] (* Vladimir Joseph Stephan Orlovsky, Jun 09 2011 *)

PROG

(MAGMA) [5*3^n: n in [0..30]]; // Vincenzo Librandi, Jun 10 2011

(PARI) a(n)=5*3^n \\ Charles R Greathouse IV, Oct 07 2015

CROSSREFS

Sequence in context: A271180 A200465 A084244 * A200664 A099235 A207096

Adjacent sequences:  A005027 A005028 A005029 * A005031 A005032 A005033

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified May 29 12:57 EDT 2017. Contains 287246 sequences.