A309719 Numbers k such that 64*10^(2*k) + 8*10^k + 1 is prime.

0, 1, 3, 6, 12, 2555, 3281, 5292, 11209

Offset

1,3

Links

Table of n, a(n) for n=1..9.

Example

            73 is prime ==> a(1) = 0.
          6481 is prime ==> a(2) = 1.
        640801 = 7 * 31 * 2953.
      64008001 is prime ==> a(3) = 3.
    6400080001 = 7 * 13441 * 68023.
  640000800001 = 619 * 1033926979.
64000008000001 is prime ==> a(4) = 6.

Prog

(PARI) for(k=0, 1e3, if(ispseudoprime(64*100^k+8*10^k+1), print1(k", ")))

Crossrefs

Cf. A309738, A309742.

Sequence in context: A013563 A009788 A102966 * A332365 A257276 A248043

Adjacent sequences: A309716 A309717 A309718 * A309720 A309721 A309722

Keyword

nonn,more,base

Author

Seiichi Manyama, Aug 15 2019

Extensions

a(9) from Michael S. Branicky, Sep 04 2024

Status

approved