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A174177
Numbers k such that 10^k-2*k-1 is prime.
2
1, 5, 11, 14, 19, 55, 101, 560, 805, 3188, 4441, 25733, 37501
OFFSET
1,2
COMMENTS
a(14) > 10^5. - Robert Price, Mar 13 2015
MATHEMATICA
Select[Range[5000], PrimeQ[(10^# - 2*# - 1)] &] (* Vincenzo Librandi, Oct 05 2012 *)
PROG
(Magma) [n: n in [1..550] | IsPrime(10^n-2*n-1) ];
(PARI) for(n=1, 999, ispseudoprime(10^n-2*n-1) && print1(n", ")) \\ M. F. Hasler, Aug 06 2011
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Vincenzo Librandi, Mar 11 2010
EXTENSIONS
a(10)-a(11) from Vincenzo Librandi, Oct 05 2012
a(12)-a(13) from Robert Price, Mar 13 2015
STATUS
approved