A387245 Numbers k such that (the concatenation of the first k positive even numbers) + 1 is prime.

1, 5, 9, 24, 1400, 8915

Offset: 1

Author

Shyam Sunder Gupta, Aug 24 2025

Keywords

• base
• more
• nonn
• new

Comments

a(6) = 8915 corresponds to a 39024-digit probable prime. a(7) > 15000.

The corresponding primes are a subsequence of A210734. - Michael S. Branicky, Aug 24 2025

Examples

			5 is a term since 246810 + 1 = 246811 is prime.
		

Crossrefs

Cf. A019520, A069048, A210734.

Formula

{k | A019520(k) + 1 is prime}. - Michael S. Branicky, Aug 24 2025