A102904 Primes of the form 3^k + 20.

23, 29, 47, 101, 263, 2207, 6581, 59069, 177167, 4782989, 984770902183611232901, 174449211009120179071170527, 278128389443693511257285776231781, 7509466514979724803946715958257567

Offset: 1

Author

Roger L. Bagula, Mar 01 2005

Keywords

• nonn

Comments

The sequence of the corresponding k starts 1, 2, 3, 4, 5, 7, 8, 10, 11, 14, 44, 55, 68, 71, 80, 123, 158, 213, 220, 272, 668, 725, 885, 1132, 1677, 2056, ... [Joerg Arndt, Jul 19 2012]

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..23

Crossrefs

Cf. A000040, A000960, A219040 (corresponding k's).

Programs

Magma

[ a: n in [0..100] | IsPrime(a) where a is 3^n+20 ]; // Vincenzo Librandi, Jul 19 2012

Mathematica

Select[Table[3^n+20, {n,0,200}],PrimeQ] (* Vincenzo Librandi, Jul 19 2012 *)

Formula

a(n) = 3^A219040(n) + 20. - Elmo R. Oliveira, Nov 12 2023