A261067 a(n) = (11^(2^n) - 1)/2^(n + 2).

15, 915, 6698715, 717964529118315, 16495138082306681918325119173515, 17413733142679306233865281770975943513633443105435651232476307915

Offset: 1

Author

Marco Ripà, Aug 08 2015

Keywords

• nonn
• easy

Comments

(m^(2^n) - 1)/2^(n + 2) is an integer for any odd value of m and n > 0.

In particular, for m = 11, a(n) is a multiple of 15.

Examples

			a(3) = (11^8 - 1)/2^5 = 6698715.
		

Crossrefs

Cf. A059723, A068531, A068533, A097421.

Programs

Magma

[(11^(2^n)-1)/2^(n+2): n in [1..6]]; // Vincenzo Librandi, Aug 14 2015

Maple

A261067:=n->(11^(2^n) - 1)/2^(n + 2): seq(A261067(n), n=1..8); # Wesley Ivan Hurt, Jan 27 2017

Mathematica

Table[(11^(2^n) - 1)/2^(n + 2), {n, 10}] (* Vincenzo Librandi, Aug 14 2015 *)

PARI

first(m)=vector(m,i, (11^(2^i)-1)/2^(i+2)); /* Anders Hellström, Aug 08 2015 */

Formula

a(n) = 15*A068533(n). - Michel Marcus, Aug 14 2015