A309582 Numbers k such that 36*10^(2*k) + 6*10^k + 1 is prime.

0, 10, 118, 138, 1143, 16344, 19324

Offset: 1

Author

Seiichi Manyama, Aug 15 2019

Keywords

• nonn
• more
• base

Comments

a(6) > 6000. - Tyler NeSmith, Dec 05 2021

Examples

			                    43 is prime ==> a(1) = 0.
                  3661 = 7 * 523.
                360601 = 19 * 18979.
              36006001 = 67 * 537403.
            3600060001 = 457 * 7877593.
          360000600001 = 7 * 51428657143.
        36000006000001 = 379 * 94986823219.
      3600000060000001 = 7 * 43 * 64609 * 185115589.
    360000000600000001 = 19 * 18947368452631579.
  36000000006000000001 = 307 * 1249 * 1071121 * 87652267.
3600000000060000000001 is prime ==> a(2) = 10.
		

Crossrefs

Cf. A309738.

Programs

PARI

for(k=0, 1e3, if(ispseudoprime(36*100^k+6*10^k+1), print1(k", ")))

Extensions

a(6) from Michael S. Branicky, Apr 24 2023

a(7) from Michael S. Branicky, Sep 07 2024