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

4, 8, 10, 42, 452, 1014

Offset

1,1

Comments

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

Links

Table of n, a(n) for n=1..6.

Example

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

Mathematica

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

Crossrefs

Cf. A066811.

Sequence in context: A323151 A037004 A136861 * A316505 A293597 A131803

Adjacent sequences: A109442 A109443 A109444 * A109446 A109447 A109448

Keyword

base,nonn

Author

Ryan Propper, Aug 26 2005

Status

approved