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

Offset: 0

Author

Omar E. Pol, Apr 27 2008

Keywords

• easy
• nonn

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).

Crossrefs

Cf. A016993, A057145, A139600.

Programs

Magma

[15*(7*n + 1): n in [0..60]]; // Vincenzo Librandi, Jul 23 2011

Mathematica

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

PARI

a(n)=105*n+15 \\ Charles R Greathouse IV, Oct 05 2011

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)