A013806 a(n) = 17^(4*n+1).

17, 1419857, 118587876497, 9904578032905937, 827240261886336764177, 69091933913008732880827217, 5770627412348402378939569991057, 481968572106750915091411825223071697, 40254497110927943179349807054456171205137

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Comments

As phi(a(n)) = (2*17^n)^4 is a perfect biquadrate (where phi is the Euler totient A000010), this is a subsequence of A078164 and A307690. - Bernard Schott, Mar 29 2022

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..100
• Tanya Khovanova, Recursive Sequences.
• Index entries for linear recurrences with constant coefficients, signature (83521).

Crossrefs

Cf. A000010, A013776, A307690.

Intersection of A001026 and A078164.

Programs

Magma

[17^(4*n+1): n in [0..15]]; // Vincenzo Librandi, Jul 06 2011

Mathematica

17^(4Range[0,10]+1) (* or *) NestList[83521#&,17,20] (* Harvey P. Dale, May 21 2013 *)

Formula

a(0)=17, a(n)=83521*a(n-1). - Harvey P. Dale, May 21 2013

Sum_{n>=0} 1/a(n) = 4913/83520. - Bernard Schott, Mar 29 2022

Sum_{n>=0} (-1)^n/a(n) = 4913/83522. - Bernard Schott, Apr 08 2022