A099082 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A099082

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

1, 5, 9, 11, 65, 159

(list; graph; refs; listen; history; text; internal format)

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

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

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