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 A110053 Numbers n such that the string 111n is the decimal expansion of a prime number. 2
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..2500 EXAMPLE 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. MAPLE 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: seq(a(n), n=1..100);  # Alois P. Heinz, Jul 30 2014 MATHEMATICA 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 *) PROG (MAGMA) [ n: n in [1..600] | IsPrime(Seqint(Intseq(n) cat [1, 1, 1])) ]; CROSSREFS Sequence in context: A231607 A147603 A106084 * A276045 A230039 A226138 Adjacent sequences:  A110050 A110051 A110052 * A110054 A110055 A110056 KEYWORD nonn,base AUTHOR Parthasarathy Nambi, Sep 04 2005 EXTENSIONS More terms from Alonso del Arte, Sep 06 2005 STATUS approved

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Last modified June 21 06:55 EDT 2021. Contains 345358 sequences. (Running on oeis4.)