A099081 Numbers k such that 1.2. ... .k-1.k + 1 is prime (where dot between numbers means concatenation).

1, 2, 6, 30, 88

Offset: 1

Author

Farideh Firoozbakht, Oct 23 2004

Keywords

• base
• more
• nonn

Comments

a(6) > 25000. - Michael S. Branicky, Sep 13 2024

Examples

			6 is in the sequence because 123456+1 is prime.
		

Crossrefs

Cf. A099082, A099083.

Programs

Mathematica

f[n_] := Block[{p = 0, k = 1}, While[k <= n, p = 10^Floor[ Log[10, k] + 1]p + k; k++ ]; PrimeQ[p + 1]]; Do[ If[ f[n], Print[n]], {n, 1000}] (* Robert G. Wilson v, Nov 01 2004 *)