A364644 Numbers k such that floor(10^k/7) is prime.

7, 25, 355, 823

Offset: 1

Author

Robert Israel, Jul 31 2023

Keywords

• nonn
• more
• hard

Comments

Numbers k such that A090519(k) = 7.

All terms == 1 (mod 6).

Numbers k such that (10^k-3)/7 is prime.

a(5) > 20000 if it exists. - Hugo Pfoertner, Jul 31 2023

Examples

			a(1) = 7 is a term because floor(10^7/7) = 1428571 is prime.
		

Crossrefs

Cf. A090519.

Programs

Maple

select(n -> isprime(floor(10^n/7)),[seq(i,i=1..1000,6)]);