A369613 Numbers k such that ceiling(10^k/7) is prime.

1, 4, 10, 16, 130, 1900, 5356, 181960

Offset: 1

Author

Jon E. Schoenfield, Jan 27 2024

Keywords

• nonn
• more
• hard

Comments

a(n) == 4 (mod 6) for n > 1.

1 and numbers k such that (10^k + 3)/7 is prime.

Examples

			4 is a term because ceiling(10^4/7) = 1429 is prime.
.
  n | k = a(n) | ceiling(10^k/7)
  --+----------+-----------------
  1 |     1    | 2
  2 |     4    | 1429
  3 |    10    | 1428571429
  4 |    16    | 1428571428571429
		

Crossrefs

Cf. A364644.

Extensions

a(8) from Jinyuan Wang, Nov 30 2024