A160869 a(n) = sigma(6^(n-1)).

1, 12, 91, 600, 3751, 22932, 138811, 836400, 5028751, 30203052, 181308931, 1088123400, 6529545751, 39179682372, 235085301451, 1410533397600, 8463265086751, 50779784492892, 304679288612371, 1828077476115000, 10968470088963751, 65810836228506612

Offset

1,2

Links

Colin Barker, Table of n, a(n) for n = 1..1000

J. H. Kwak and J. Lee, Enumeration of graph coverings, surface branched coverings and related group theory, in Combinatorial and Computational Mathematics (Pohang, 2000), ed. S. Hong et al., World Scientific, Singapore 2001, pp. 97-161.

Index entries for linear recurrences with constant coefficients, signature (12,-47,72,-36).

Formula

a(n) = A059387(n)/2. - Vladimir Joseph Stephan Orlovsky, Apr 28 2010

a(n) = 12*a(n-1)-47*a(n-2)+72*a(n-3)-36*a(n-4). - Colin Barker, Nov 24 2014

G.f.: -x*(6*x^2-1) / ((x-1)*(2*x-1)*(3*x-1)*(6*x-1)). - Colin Barker, Nov 24 2014

a(n) = A000203(A000400(n-1)). - Michel Marcus, Sep 18 2018

Mathematica

Table[(2^n-1)*(3^n-1)/2, {n, 40}] (* Vladimir Joseph Stephan Orlovsky, Apr 28 2010 *)
LinearRecurrence[{12, -47, 72, -36}, {1, 12, 91, 600}, 50] (* G. C. Greubel, Apr 30 2018 *)

Prog

(PARI) Vec(-x*(6*x^2-1)/((x-1)*(2*x-1)*(3*x-1)*(6*x-1)) + O(x^100)) \\ Colin Barker, Nov 24 2014
(PARI) for(n=1, 50, print1((2^n-1)*(3^n-1)/2, ", ")) \\ G. C. Greubel, Apr 30 2018
(Magma) [(2^n-1)*(3^n-1)/2: n in [1..50]]; // G. C. Greubel, Apr 30 2018

Crossrefs

Row 6 of array in A160870.

Cf. A000203, A000400, A059387.

Sequence in context: A001502 A001503 A004311 * A026074 A339715 A298397

Adjacent sequences: A160866 A160867 A160868 * A160870 A160871 A160872

Keyword

nonn,easy

Author

N. J. A. Sloane, Nov 15 2009

Extensions

More terms from Vladimir Joseph Stephan Orlovsky, Apr 28 2010

More terms from Colin Barker, Nov 24 2014

Better definition from Altug Alkan, Oct 06 2015

Status

approved