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 A107644 Numbers n such that the string 1113n is the decimal expansion of a prime number. 5
 1, 17, 23, 37, 41, 47, 73, 103, 137, 149, 157, 173, 181, 187, 193, 197, 199, 221, 239, 253, 257, 317, 319, 337, 349, 373, 379, 401, 403, 421, 451, 461, 481, 491, 509, 521, 527, 557, 569, 587, 599, 617, 643, 667, 701, 703, 713, 719, 751, 773, 781, 787, 793 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 11 and 13 are twin primes. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 EXAMPLE n=1: 11131 is prime. n=47: 111347 is prime. n=149: 1113149 is prime. MATHEMATICA Select[Range[800], PrimeQ[1113*10^IntegerLength[#]+#]&] (* Harvey P. Dale, Sep 26 2016 *) PROG (MAGMA) [ n: n in [1..800] | IsPrime(Seqint(Intseq(n) cat [3, 1, 1, 1])) ]; CROSSREFS Sequence in context: A080830 A165566 A072184 * A158710 A103805 A241528 Adjacent sequences:  A107641 A107642 A107643 * A107645 A107646 A107647 KEYWORD nonn,base AUTHOR Parthasarathy Nambi, Jun 09 2005 STATUS approved

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Last modified July 19 22:14 EDT 2019. Contains 325168 sequences. (Running on oeis4.)