A109445 Numbers k such that (concatenation of even integers through k) - 1 is a prime.

4, 8, 10, 42, 452, 1014

Offset: 1

Author

Ryan Propper, Aug 26 2005

Keywords

• base
• nonn
• more
• changed

Comments

Next term is greater than 2000. All terms less than 1000 correspond to certified primes (Primo 2.2.0 beta).

Next term is greater than 20000. - Michael S. Branicky, Aug 28 2025

Examples

			4 is a term because 24 - 1 = 23 is prime.
8 is a term because 2468 - 1 = 2467 is prime.
		

Crossrefs

Cf. A066811.

Programs

Mathematica

p = ""; Do[p = p <> ToString[2*n]; If[PrimeQ[ToExpression[p] - 1], Print[2*n]], {n, 1, 10^3}]