A002958 Numbers k such that 2*25^k - 1 is prime. (Formerly M0870)

2, 3, 8, 12, 15, 27, 48, 89, 137, 666, 1383, 1530, 2102, 8868, 95031, 111768, 130200, 341540

Offset

1,1

References

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

C. R. Zarnke and H. C. Williams, Computer determination of some large primes, pp. 563-570 in Proceedings of the Louisiana Conference on Combinatorics, Graph Theory and Computer Science. Vol. 2, edited R. C. Mullin et al., 1971.

Links

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

Mathematica

Do[m = n; If[PrimeQ[2*25^n - 1], Print[n]], {n, 1, 10^3}]
Select[Range[0, 5000], PrimeQ[(2*25^# - 1)] &] (* Vincenzo Librandi, Sep 25 2012 *)

Prog

(PARI) is(n)=ispseudoprime(2*25^n-1) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Sequence in context: A192113 A243192 A164817 * A290153 A266629 A249096

Adjacent sequences: A002955 A002956 A002957 * A002959 A002960 A002961

Keyword

nonn,hard,more

Author

N. J. A. Sloane, Simon Plouffe

Extensions

a(10) from Robert G. Wilson v, Nov 02 2000

a(11)-a(13) from Vincenzo Librandi, Sep 25 2012

a(14)-a(17) (from A120375) from Joerg Arndt, Jun 15 2020

a(18) (from A120375) by Jorge Coveiro, Jun 20 2020

Status

approved