A309743 Numbers k such that 9*10^(2*k) + 9*10^k + 1 is prime.

0, 1, 2, 6, 12, 245, 298, 2967, 4321, 7225, 11267

Offset

1,3

Comments

a(12) > 2*10^4. - Tyler Busby, Jan 07 2023

Links

Table of n, a(n) for n=1..11.

Example

           19 is prime. ==> a(1) = 0.
          991 is prime. ==> a(2) = 1.
        90901 is prime. ==> a(3) = 2.
      9009001 = 131 * 68771.
    900090001 = 421 * 2137981.
  90000900001 = 131 * 701 * 980071.
9000009000001 is prime. ==> a(4) = 6.

Prog

(PARI) for(k=0, 1e3, if(ispseudoprime(9*100^k+9*10^k+1), print1(k", ")))

Crossrefs

Cf. A309739.

Sequence in context: A105122 A351940 A132076 * A291062 A058046 A298410

Adjacent sequences: A309740 A309741 A309742 * A309744 A309745 A309746

Keyword

nonn,more

Author

Seiichi Manyama, Aug 15 2019

Extensions

a(10)-a(11) from Tyler Busby, Jan 07 2023

Status

approved