A007648 n*18^n + 1 is a prime.

1, 3, 21, 23, 842, 1683, 3401, 16839, 49963, 60239, 150940, 155928

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• hard

Comments

a(13) > 203597. - Ray Chandler, Apr 10 2016

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).

Programs

Mathematica

k = 0; While[k < 10001, If[PrimeQ[k*18^k + 1], Print@ k]; k++] (* Robert G. Wilson v, Aug 19 2013 *)

Extensions

Error in description corrected 8/97.

a(7) from Robert G. Wilson v, Dec 10 2012

a(8)-a(10) from Giovanni Resta, Aug 21 2013

a(11)-a(12) from Loeh link by Ray Chandler, Apr 10 2016