login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A138051 Numbers k such that 27^k + 2 is prime. 7
0, 1, 5, 8, 12, 21, 41, 42, 81, 105, 121, 377, 501, 2401, 14597, 35381, 59476, 120536 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

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

Conjecture: 3^3^n+2 does not meet anti Fermat's conjecture. - Vincenzo Librandi, Aug 01 2010

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 = Numbers n such that 3^n + 2 is prime. Cf. A087885 = Numbers n such that 5^n + 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

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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 14 06:59 EDT 2021. Contains 342946 sequences. (Running on oeis4.)