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

1,2

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

Links

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

Example

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

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 *)

Crossrefs

Cf. A007908, A099081, A099083.

Sequence in context: A288143 A120228 A053749 * A062217 A331053 A314605

Adjacent sequences: A099079 A099080 A099081 * A099083 A099084 A099085

Keyword

base,more,nonn

Author

Farideh Firoozbakht, Oct 23 2004

Status

approved