A109371 Numbers k such that the string 11k is prime.

3, 17, 23, 29, 51, 53, 63, 71, 81, 87, 93, 113, 117, 119, 131, 149, 159, 161, 171, 173, 177, 197, 213, 239, 243, 251, 257, 261, 273, 279, 287, 299, 311, 317, 321, 329, 351, 353, 369, 383, 393, 399, 411, 423, 437, 443, 447, 467, 471, 483, 489, 491, 497, 503

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..2000

Example

If k=3 then 11k = 113, which is prime.
If k=87 then 11k = 1187, which is prime.

Maple

a:= proc(n) local k; for k from 1 +`if`(n=1, 0, a(n-1))
      while not isprime(parse(""||11||k)) do od; a(n):=k
    end:
seq(a(n), n=1..100);  # Alois P. Heinz, Jul 30 2014

Mathematica

Select[Range[800], PrimeQ[11 10^IntegerLength[#] + #] &] (* Vincenzo Librandi, Jul 30 2014 *)

Prog

(Magma) [n: n in [1..600] | IsPrime(Seqint(Intseq(n) cat [1, 1])) ]; // Vincenzo Librandi, Jul 30 2014

Crossrefs

Sequence in context: A296937 A126692 A057173 * A272176 A082372 A273407

Adjacent sequences: A109368 A109369 A109370 * A109372 A109373 A109374

Keyword

nonn,base

Author

Parthasarathy Nambi, Aug 24 2005

Extensions

More terms from Vincenzo Librandi, Mar 27 2010

Status

approved