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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
OFFSET
1,1
LINKS
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
KEYWORD
nonn,base
AUTHOR
Parthasarathy Nambi, Aug 24 2005
EXTENSIONS
More terms from Vincenzo Librandi, Mar 27 2010
STATUS
approved