A193448 a(n) = 4*(5*n^2 - 5*n + 1).

4, 44, 124, 244, 404, 604, 844, 1124, 1444, 1804, 2204, 2644, 3124, 3644, 4204, 4804, 5444, 6124, 6844, 7604, 8404, 9244, 10124, 11044, 12004, 13004, 14044, 15124, 16244, 17404, 18604, 19844, 21124, 22444, 23804, 25204, 26644, 28124, 29644, 31204, 32804

Offset: 1

Author

Giovanni Teofilatto, Jul 26 2011

Keywords

• nonn
• easy

Comments

The natural numbers of the form 5*n^2-1, with n odd. See also A158491 for the cases where n is even. - Giovanni Teofilatto, Oct 10 2011

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..10000
• Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

Crossrefs

Cf. A062786, A158491.

Programs

Magma

[4*(5*n^2-5*n+1): n in [1..50]]; // Vincenzo Librandi, Aug 30 2011

Maple

A193448:=n->4*(5*n^2 - 5*n + 1): seq(A193448(n), n=1..50); # Wesley Ivan Hurt, Nov 21 2015

Mathematica

Table[4*(5*n^2 - 5*n + 1), {n, 50}] (* Wesley Ivan Hurt, Nov 21 2015 *)

PARI

a(n) = 4*(5*n^2 - 5*n + 1) \\ Anders Hellström, Nov 21 2015

Formula

a(n) = 4*A062786(n).

G.f.: -4*x*(1+8*x+x^2) / (x-1)^3. - R. J. Mathar, Aug 26 2011

a(n) = 3*a(n-1)-3*a(n-2)+a(n-3) for n>3. - Wesley Ivan Hurt, Nov 21 2015