A289723 Primes of the form 3^k - 20.

7, 61, 223, 709, 59029, 177127, 1162261447, 3486784381, 94143178807, 847288609423, 2541865828309, 7509466514979724803946715958257527, 147808829414345923316083210206383297581, 26183890704263137277674192438430182020124327

Offset: 1

Author

Robert Price, Sep 02 2017

Keywords

• nonn

Links

• Robert Price, Table of n, a(n) for n = 1..20
• F. Firoozbakht, M. F. Hasler, Variations on Euclid's formula for Perfect Numbers, JIS 13 (2010) #10.3.1.
• Henri & Renaud Lifchitz, PRP Records
• OpenPFGW Project, Primality Tester

Crossrefs

Cf. A000040, A219041 (corresponding k's).

Programs

Mathematica

Select[Table[3^k - 20, {k, 3, 100}], PrimeQ[#] &]

Formula

a(n) = 3^A219041(n) - 20. - Elmo R. Oliveira, Nov 09 2023