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

Author

Juri-Stepan Gerasimov, Sep 23 2011

Keywords

• nonn
• more

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

a(19) > 10^5, if it exists. - Michael S. Branicky, Aug 26 2024

Examples

			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.
		

Crossrefs

Cf. A048473.

Programs

PARI

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

Extensions

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