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A110053
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Numbers n such that the string 111n is the decimal expansion of a prime number.
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2
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7, 13, 17, 19, 31, 49, 59, 61, 71, 73, 77, 97, 103, 109, 119, 121, 127, 143, 149, 187, 191, 211, 217, 227, 229, 253, 263, 269, 271, 301, 317, 323, 337, 341, 347, 373, 409, 427, 431, 439, 443, 467, 487, 491, 493, 497, 509, 521, 533, 539, 577, 581, 593, 599
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OFFSET
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1,1
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LINKS
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EXAMPLE
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7 is in the sequence because 1117 is prime.
73 is in the sequence because 11173 is prime.
103 is in the sequence because 111103 is prime.
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MAPLE
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a:= proc(n) local k; for k from 1 +`if`(n=1, 0, a(n-1))
while not isprime(parse(""||111||k)) do od; a(n):=k
end:
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MATHEMATICA
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Select[Range[1000], PrimeQ[FromDigits[Join[{1, 1, 1}, IntegerDigits[ # ]]]] &] (* _Alonso Delarte_, Sep 06 2005 *)
Select[Range[600], PrimeQ[111 10^IntegerLength[#] + #] &] (* Vincenzo Librandi, Jul 30 2014 *)
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PROG
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(Magma) [ n: n in [1..600] | IsPrime(Seqint(Intseq(n) cat [1, 1, 1])) ];
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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