A013768 a(n) = 21^(3*n + 1).

21, 194481, 1801088541, 16679880978201, 154472377739119461, 1430568690241985328321, 13248496640331026125580781, 122694327386105632949003612841, 1136272165922724266740722458520501, 10523016528610349434285830688358359761

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..200
• Tanya Khovanova, Recursive Sequences
• Index entries for linear recurrences with constant coefficients, signature (9261).

Crossrefs

Subsequence of A009965.

Programs

Magma

[21^(3*n+1): n in [0..10]]; // Vincenzo Librandi, Jun 27 2011

Mathematica

21^(3*Range[0,10]+1) (* or *) NestList[9261#&,21,10] (* Harvey P. Dale, Apr 30 2020 *)

PARI

a(n)=21^(3*n+1) \\ Charles R Greathouse IV, Jul 10 2016