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

Author

Seiichi Manyama, Aug 15 2019

Keywords

• nonn
• more
• base

Examples

			            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.
		

Crossrefs

Cf. A309738, A309742.

Programs

PARI

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

Extensions

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