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

1, 2, 6, 30, 88

Offset

1,2

Links

Table of n, a(n) for n=1..5.

Example

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

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 *)

Crossrefs

Cf. A099082, A099083.

Sequence in context: A328417 A290760 A088857 * A051844 A335396 A034501

Adjacent sequences: A099078 A099079 A099080 * A099082 A099083 A099084

Keyword

base,more,nonn

Author

Farideh Firoozbakht, Oct 23 2004

Status

approved