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A099081
Numbers k such that 1.2. ... .k-1.k + 1 is prime (where dot between numbers means concatenation).
4
1, 2, 6, 30, 88
OFFSET
1,2
COMMENTS
a(6) > 25000. - Michael S. Branicky, Sep 13 2024
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
Sequence in context: A328417 A290760 A088857 * A051844 A335396 A034501
KEYWORD
base,more,nonn
AUTHOR
Farideh Firoozbakht, Oct 23 2004
STATUS
approved