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 A272271 Numbers k such that 7*10^k - 23 is prime. 0
 1, 2, 3, 23, 29, 34, 35, 38, 52, 57, 61, 82, 186, 209, 251, 366, 394, 426, 786, 979, 1382, 2037, 4557, 8995, 12774, 19170, 21828, 23259, 32003, 41831, 44999, 56785, 76483, 97987, 110468 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 9 followed by the digits 77 is prime (see Example section). a(36) > 3*10^5. LINKS Table of n, a(n) for n=1..35. Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 69w77. EXAMPLE 3 is in this sequence because 7*10^3 - 23 = 6977 is prime. Initial terms and associated primes: a(1) = 1, 47; a(2) = 2, 677; a(3) = 3, 6977; a(4) = 23, 699999999999999999999977; a(5) = 29, 699999999999999999999999999977, etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[7*10^# - 23] &] PROG (PARI) is(n)=ispseudoprime(7*10^n - 23) \\ Charles R Greathouse IV, Jun 13 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A280894 A042585 A143279 * A068887 A364142 A260128 Adjacent sequences: A272268 A272269 A272270 * A272272 A272273 A272274 KEYWORD nonn,more AUTHOR Robert Price, Apr 24 2016 EXTENSIONS a(35) from Robert Price, Jul 27 2019 STATUS approved

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Last modified June 20 03:21 EDT 2024. Contains 373512 sequences. (Running on oeis4.)