A099082 Numbers k such that 1.2. ... .k-1.k + 2 is prime (dot between numbers means concatenation).

1, 5, 9, 11, 65, 159

Offset: 1

Author

Farideh Firoozbakht, Oct 23 2004

Keywords

• base
• more
• nonn

Comments

Numbers k such that A007908(k)+2 is prime.

Next term is greater than 2000.

a(7) > 4034. - J.W.L. (Jan) Eerland, Nov 19 2022

a(7) > 15176. - J.W.L. (Jan) Eerland, Feb 24 2023

a(7) > 30000. - Michael S. Branicky, Sep 13 2024

Examples

			9 is in the sequence because 123456789 + 2 is prime.
		

Crossrefs

Cf. A007908, A099081, A099083.

Programs

Mathematica

n=0;Monitor[Parallelize[While[True,If[PrimeQ[2+ToExpression[StringJoin[ToString/@Table[k,{k,1,n}]]]],Print[n]];n++];n],n] (* J.W.L. (Jan) Eerland, Nov 19 2022 *)