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A089379
Numbers k such that 10^k + k is prime.
2
1, 9, 69, 313, 451, 13807, 23769
OFFSET
1,2
COMMENTS
a(8) > 10^5. - Robert Price, Feb 14 2015
EXAMPLE
a(2)=9 because 10^9 + 9 is prime.
MATHEMATICA
Do[If[Mod[n, 3]!=2&& PrimeQ[10^n+n], Print[n]], {n, 1, 15500, 2}] (* Farideh Firoozbakht, Jun 11 2006 *)
PROG
(PARI) is(n)=ispseudoprime(10^n+n) \\ Charles R Greathouse IV, Jun 12 2017
CROSSREFS
Cf. A110066.
Sequence in context: A348590 A120306 A197425 * A193698 A188800 A297393
KEYWORD
nonn
AUTHOR
Shyam Sunder Gupta, Dec 27 2003
EXTENSIONS
One more term from Farideh Firoozbakht, Jun 11 2006
a(7) from Robert Price, Feb 14 2015
STATUS
approved