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A139615

a(n) = 105*n + 15.

15, 120, 225, 330, 435, 540, 645, 750, 855, 960, 1065, 1170, 1275, 1380, 1485, 1590, 1695, 1800, 1905, 2010, 2115, 2220, 2325, 2430, 2535, 2640, 2745, 2850, 2955, 3060, 3165, 3270, 3375, 3480, 3585, 3690, 3795, 3900, 4005, 4110, 4215

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OFFSET

0,1

COMMENTS

Numbers of the 15th column of positive numbers in the square array of nonnegative and polygonal numbers A139600. Also, numbers of the 15th column in the square array A057145.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..5000

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

FORMULA

From Elmo R. Oliveira, Apr 04 2024: (Start)

G.f.: 15*(1+6*x)/(x-1)^2.

E.g.f.: 15*exp(x)*(1 + 7*x).

a(n) = 15*A016993(n).

a(n) = 2*a(n-1) - a(n-2) for n >= 2. (End)

MATHEMATICA

105*Range[0, 40]+15 (* or *) LinearRecurrence[{2, -1}, {15, 120}, 50] (* Harvey P. Dale, May 07 2016 *)

PROG