A309719 - OEIS

A309719

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

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

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OFFSET

1,3

LINKS

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

KEYWORD

nonn,more,base

AUTHOR

EXTENSIONS

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

STATUS

approved