A294396 Numbers k such that 12*10^k + 1 is prime.

0, 2, 38, 80, 9230, 25598, 39500

Offset: 1

Author

Patrick A. Thomas, Feb 12 2018

Keywords

• nonn
• more

Comments

k must be even since 12*10^k + 1 is divisible by 11 if k is odd. - Robert G. Wilson v, Feb 12 2018

a(7) > 27440. - Robert G. Wilson v, Feb 17 2018

a(8) > 10^5. - Jeppe Stig Nielsen, Jan 31 2023

Examples

			13 and 1201 are prime, so 0 and 2 are the initial values.
		

Crossrefs

Cf. A001562, A096507, A056797, A056807, A056806, A102940, A056805, A056804, A096508, A102975, A289051, A099017, A295325, A273002, A102945, A282456, A267420.

Cf. A062339 (primes with digit sum 4).

Programs

Mathematica

ParallelMap[ If[ PrimeQ[12*10^# +1], #, Nothing] &, 2 + 6Range@ 4500] (* Robert G. Wilson v, Feb 13 2018 *)

PARI

isok(k) = isprime(12*10^k + 1); \\ Altug Alkan, Mar 04 2018

Extensions

a(5) from Robert G. Wilson v, Feb 12 2018

a(6) from Robert G. Wilson v, Feb 13 2018

a(7) from Jeppe Stig Nielsen, Jan 28 2023