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 A280060 Numbers k such that (2*10^k + 49)/3 is prime. 0
 0, 1, 2, 3, 5, 6, 7, 8, 13, 21, 22, 25, 26, 38, 200, 395, 442, 561, 908, 1295, 5541, 7795, 8600, 19157, 22536, 45636 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS For k>1, numbers such that k-2 occurrences of the digit 6 followed by the digits 83 is prime (see Example section). a(27) > 2*10^5. LINKS Table of n, a(n) for n=1..26. Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 6w83. EXAMPLE 3 is in this sequence because (2*10^3 + 49) / 3 = 683 is prime. Initial terms and primes associated: a(1) = 0, 17; a(2) = 1, 23; a(3) = 2, 83; a(4) = 3, 683; a(5) = 5, 66683; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(2*10^# + 49) / 3] &] PROG (PARI) is(n)=ispseudoprime((2*10^n + 49)/3) \\ Charles R Greathouse IV, Jun 13 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A068526 A287339 A039086 * A197433 A153781 A255398 Adjacent sequences: A280057 A280058 A280059 * A280061 A280062 A280063 KEYWORD nonn,more,hard AUTHOR Robert Price, Jan 04 2017 STATUS approved

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Last modified September 28 19:13 EDT 2023. Contains 365737 sequences. (Running on oeis4.)