A138051 Numbers k such that 27^k + 2 is prime.

0, 1, 5, 8, 12, 21, 41, 42, 81, 105, 121, 377, 501, 2401, 14597, 35381, 59476, 120536

Offset

1,3

Comments

All terms are the exact thirds of terms of A051783 that are divisible by 3.

Links

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

Henri & Renaud Lifchitz, PRP Records.

Mathematica

Do[ f = 27^n + 2; If[ PrimeQ[ f ], Print[ {n, f} ] ], {n, 1, 2500} ]

Prog

(PARI) is(n)=ispseudoprime(27^n+2) \\ Charles R Greathouse IV, Feb 17 2017

Crossrefs

Cf. A051783 (3^k + 2 is prime), A087885 (5^k + 2 is prime).

Cf. A090649, A109076, A113480, A138048, A138049, A138050, A087886, A113481.

Cf. A176495.

Sequence in context: A115072 A114644 A314419 * A026279 A260966 A338547

Adjacent sequences: A138048 A138049 A138050 * A138052 A138053 A138054

Keyword

nonn,more

Author

Alexander Adamchuk, Mar 02 2008

Extensions

a(15)-a(17) from A051783 by Ray Chandler, Aug 06 2011

a(18) from Robert Price, May 12 2019

Status

approved