

A195732


Numbers n such that 2*(3^nn)1 is prime.


1




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..9.


EXAMPLE

1 is in the sequence because 2*3^12*11 = 3 is a prime, 2 is in the sequence because 2*3^22*21 = 13 is a prime, 3 is in the sequence because 2*3^32*31=47 ts a prime, 4 is not in the sequence because 2*3^42*41 = 153 = 3^2*17 is not prime.


PROG

(PARI) is(n)=ispseudoprime(2*(3^nn)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


AUTHOR

JuriStepan Gerasimov, Sep 23 2011


STATUS

approved



