A006553 Numbers k such that k*3^k - 1 is prime.

1, 2, 6, 10, 18, 40, 46, 86, 118, 170, 1172, 1698, 1810, 2268, 4338, 18362, 72662, 88392, 94110, 161538, 168660, 292340, 401208, 560750, 1035092

Offset: 1

Author

N. J. A. Sloane

Keywords

• hard
• nonn

References

• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• Steven Harvey, Generalized Woodall Search

Programs

Magma

[n: n in [0..1420] | 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 20 2017

Extensions

More terms from Jud McCranie

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

a(24)-a(25) from Harvey link by Ray Chandler, Apr 10 2016