A037621 - OEIS

A037621

Base 7 digits are, in order, the first n terms of the periodic sequence with initial period 2,0,3.

2, 14, 101, 709, 4963, 34744, 243210, 1702470, 11917293, 83421053, 583947371, 4087631600, 28613421202, 200293948414, 1402057638901, 9814403472309, 68700824306163, 480905770143144, 3366340391002010, 23564382737014070, 164950679159098493, 1154654754113689453, 8082583278795826171

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..23.

Index entries for linear recurrences with constant coefficients, signature (7,0,1,-7).

FORMULA

G.f.: x*(2 + 3*x^2)/((x - 1)*(7*x - 1)*(1 + x + x^2)). - R. J. Mathar, Apr 29 2015

E.g.f.: (101*exp(7*x) - 95*exp(x) - exp(-x/2)*(6*cos(sqrt(3)*x/2) - 46sqrt(3)*sin(sqrt(3)*x/2)))/342. - Stefano Spezia, Oct 07 2025

MAPLE

a:= proc(n) option remember; `if`(n=0, 0,

a(n-1)*7+[3, 2, 0][1+irem(n, 3)])