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A099082
Numbers k such that 1.2. ... .k-1.k + 2 is prime (dot between numbers means concatenation).
3
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
a(7) > 30000. - Michael S. Branicky, Sep 13 2024
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
KEYWORD
base,more,nonn
AUTHOR
Farideh Firoozbakht, Oct 23 2004
STATUS
approved