Voozh

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

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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: