A006552 Numbers k such that k*3^k + 1 is prime.

2, 8, 32, 54, 114, 414, 1400, 1850, 2848, 4874, 7268, 19290, 337590, 1183414

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• hard

References

• H. Dubner, Generalized Cullen numbers, J. Rec. Math., 21 (No. 3, 1989), 190-191.
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• H. Dubner, Generalized Cullen numbers, J. Rec. Math., 21 (No. 3, 1989), 190-191. (Annotated scanned copy)
• G. Loeh, Generalized Cullen primes

Programs

Magma

[n: n in [0..420] | IsPrime(n*3^n+1)]; // Vincenzo Librandi, Dec 02 2015

Mathematica

Select[Range[10000], PrimeQ[# 3^# + 1] &] (* Vincenzo Librandi, Dec 02 2015 *)

PARI

is(n)=ispseudoprime(n*3^n+1) \\ Charles R Greathouse IV, Feb 17 2017

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008

a(14) from Loeh link by Ray Chandler, Apr 10 2016