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A109371 Numbers k such that the string 11k is prime. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified August 20 02:06 EDT 2019. Contains 326136 sequences. (Running on oeis4.)