A051156 a(n) = (2^p^2 - 1)/(2^p - 1) where p is the n-th prime.

5, 73, 1082401, 4432676798593, 1298708349570020393652962442872833, 91355004067076339167413824240109498970069278721, 7588608256743087977590500540116743445925584618982806531428980886590618779326218241

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Comments

Note that a(n) = Phi(p,2^p) or a(n) = Phi(p^2,2), where Phi(m,x) is the m-th cyclotomic polynomial and p is the n-th prime. - Thomas Ordowski, Feb 18 2014

Crossrefs

Cf. A051154, A051155, A051157.

Programs

Mathematica

Table[Cyclotomic[Prime[n]^2, 2], {n, 7}] (* Arkadiusz Wesolowski, May 13 2012 *)
Table[(2^Prime[n]^2-1)/(2^Prime[n]-1),{n,10}] (* Harvey P. Dale, Apr 06 2019 *)

Formula

a(n) = A070526(prime(n)), a(n) = A019320(prime(n)^2). - Thomas Ordowski, Feb 18 2014