A309741 Numbers k such that 6*10^(2*k) + 6*10^k + 1 is prime.

0, 1, 2, 4, 22, 133, 567, 14739, 25390

Offset

1,3

Links

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

Example

       13 is prime. ==> a(1) = 0.
      661 is prime. ==> a(2) = 1.
    60601 is prime. ==> a(3) = 2.
  6006001 = 2027 * 2963.
600060001 is prime. ==> a(4) = 4.

Prog

(PARI) for(k=0, 1e3, if(ispseudoprime(6*100^k+6*10^k+1), print1(k", ")))

Crossrefs

Cf. A309739.

Sequence in context: A235938 A279705 A321248 * A110130 A259116 A283322

Adjacent sequences: A309738 A309739 A309740 * A309742 A309743 A309744

Keyword

nonn,more,base

Author

Seiichi Manyama, Aug 15 2019

Extensions

a(8)-a(9) from Michael S. Branicky, Sep 03 2024

Status

approved