A195732 Numbers k such that 2*(3^k-k)-1 is prime.

1, 2, 3, 11, 30, 62, 534, 620, 803, 2436, 2669, 3975, 4530, 4827, 5294, 15987, 17589, 51960

Offset

1,2

Comments

According to Maple version 14, the next entries are 534, 620 and 803, but these involve primes of 256 and more digits and may not be certified primes. - R. J. Mathar, Sep 23 2011

Links

Table of n, a(n) for n=1..18.

Example

1 is in the sequence because 2*3^1-2*1-1 = 3 is a prime, 2 is in the sequence because 2*3^2-2*2-1 = 13 is a prime, 3 is in the sequence because 2*3^3-2*3-1=47 ts a prime, 4 is not in the sequence because 2*3^4-2*4-1 = 153 = 3^2*17 is not prime.

Prog

(PARI) is(n)=ispseudoprime(2*(3^n-n)-1) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Cf. A048473.

Sequence in context: A003455 A103275 A278209 * A038987 A142957 A191058

Adjacent sequences: A195729 A195730 A195731 * A195733 A195734 A195735

Keyword

nonn,more

Author

Juri-Stepan Gerasimov, Sep 23 2011

Extensions

a(10)-a(18) from Michael S. Branicky, Jul 14 2023

Status

approved