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

Author

Seiichi Manyama, Aug 15 2019

Keywords

• nonn
• more

Comments

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

Examples

			           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.
		

Crossrefs

Cf. A309739.

Programs

PARI

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

Extensions

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