

A128024


Numbers n such that (7^n  3^n)/4 is prime.


29




OFFSET

1,1


COMMENTS

All terms are primes. No other terms < 100,000.


LINKS

Table of n, a(n) for n=1..10.


MATHEMATICA

k=4; Select[ Prime[ Range[1, 200] ], PrimeQ[ ((k+3)^#  3^#)/k ]& ]


PROG

(PARI) forprime(p=3, 1e5, if(ispseudoprime((7^p3^p)/4), print1(p", "))) \\ Charles R Greathouse IV, Jun 01 2011


CROSSREFS

Cf. A028491 = numbers n such that (3^n  1)/2 is prime. Cf. A057468 = numbers n such that 3^n  2^n is prime. Cf. A059801 = numbers n such that 4^n  3^n is prime. Cf. A121877 = numbers n such that (5^n  3^n)/2 is a prime. Cf. A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032.
Sequence in context: A215487 A146037 A172514 * A245723 A118128 A113875
Adjacent sequences: A128021 A128022 A128023 * A128025 A128026 A128027


KEYWORD

hard,more,nonn


AUTHOR

Alexander Adamchuk, Feb 11 2007


EXTENSIONS

a(8)a(9) from Farideh Firoozbakht, Apr 08 2007
a(10) from Robert Price, Jun 01 2011


STATUS

approved



