login
A174178
Numbers n such that 10^n+2*n+1 is prime.
2
0, 1, 4, 24, 43, 94, 193, 204, 379, 405, 675, 3811, 10239, 26809
OFFSET
1,3
COMMENTS
a(15) > 10^5. - Robert Price, Mar 13 2015
MATHEMATICA
Select[Range[0, 5000], PrimeQ[(10^# + 2*# + 1)] &] (* Vincenzo Librandi, Oct 05 2012 *)
PROG
(Magma) [n: n in [0..400] | IsPrime(10^n+2*n+1)];
(PARI) is(n)=ispseudoprime(10^n+2*n+1) \\ Charles R Greathouse IV, Jun 06 2017
CROSSREFS
Cf. A173840 (associated primes).
Sequence in context: A121024 A120622 A031117 * A139245 A224242 A066770
KEYWORD
nonn,hard,more
AUTHOR
Vincenzo Librandi, Mar 11 2010
EXTENSIONS
a(10)-a(12) from Vincenzo Librandi, Oct 05 2012
Prepended a(1)=0 and added a(13)-a(14) by Robert Price, Mar 13 2015
STATUS
approved