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 A271645 Numbers n such that (23*10^n+91)/3 is prime. 0
 1, 2, 4, 15, 16, 19, 20, 26, 38, 47, 52, 75, 122, 191, 246, 257, 294, 305, 374, 592, 682, 729, 1092, 2053, 2997, 4065, 13936, 17214, 19059, 37433 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For n>1, numbers such that the digit 7 followed by n-2 occurrences of the digit 6 followed by the digits 97 is prime (see Example section). a(31) > 10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 76w97. EXAMPLE 4 is in this sequence because (23*10^4+91)/3 = 76697 is prime. Initial terms and primes associated: a(1) = 1, 107; a(2) = 2, 797; a(3) = 4, 76697; a(4) = 15, 7666666666666697; a(5) = 16, 76666666666666697, etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(23*10^#+91)/3] &] PROG (PARI) is(n)=ispseudoprime((23*10^n+91)/3) \\ Charles R Greathouse IV, Jun 13 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A196239 A019543 A304568 * A265483 A154906 A260299 Adjacent sequences:  A271642 A271643 A271644 * A271646 A271647 A271648 KEYWORD nonn,more AUTHOR Robert Price, Apr 11 2016 STATUS approved

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Last modified April 25 23:48 EDT 2019. Contains 322465 sequences. (Running on oeis4.)