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 A281911 Numbers k such that (185*10^k + 7)/3 is prime. 0
 1, 4, 5, 14, 65, 74, 131, 320, 336, 528, 2156, 2370, 2658, 2660, 4940, 6108, 7662, 17813, 20330, 22235, 24600, 26280, 40241, 43936, 72484, 75777, 89063, 166837 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k > 0, numbers k such that the digits 61 followed by k-1 occurrences of the digit 6 followed by the digit 9 is prime (see Example section). a(29) > 2*10^5. LINKS Table of n, a(n) for n=1..28. Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 616w9. EXAMPLE 5 is in this sequence because (185*10^5 + 7)/3 = 6166669 is prime. Initial terms and associated primes: a(1) = 1, 619; a(2) = 4, 616669; a(3) = 5, 6166669; a(4) = 14, 6166666666666669; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(185*10^# + 7)/3] &] PROG (PARI) isok(k) = isprime((185*10^k + 7)/3); \\ Michel Marcus, Feb 04 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A182252 A041857 A041034 * A042535 A222489 A222501 Adjacent sequences: A281908 A281909 A281910 * A281912 A281913 A281914 KEYWORD nonn,more,hard AUTHOR Robert Price, Feb 01 2017 EXTENSIONS a(28) from Robert Price, Mar 20 2020 STATUS approved

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Last modified August 10 12:34 EDT 2024. Contains 375056 sequences. (Running on oeis4.)