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 A295397 Numbers k such that (35*10^k - 737)/9 is prime. 0
 2, 7, 13, 20, 26, 73, 103, 268, 383, 527, 1748, 2848, 4424, 7933, 8311, 9700, 14872, 18218, 31294, 42032, 55547, 111232 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For k > 1, numbers such that the digit 3 followed by k-2 occurrences of the digit 8 followed by the digits 07 is prime (see Example section). a(23) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 38w07 EXAMPLE 2 is in this sequence because (35*10^2 - 737)/9 = 307 is prime. Initial terms and primes associated: a(1) = 2, 307; a(2) = 7, 38888807; a(3) = 13, 38888888888807; a(4) = 20, 388888888888888888807; a(5) = 26, 388888888888888888888888807; etc. MATHEMATICA Select[Range[2, 100000], PrimeQ[(35*10^# - 737)/9] &] PROG (PARI) isok(k) = isprime((35*10^k - 737)/9); \\ Michel Marcus, Nov 22 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A079381 A079382 A111354 * A329817 A155212 A106675 Adjacent sequences:  A295394 A295395 A295396 * A295398 A295399 A295400 KEYWORD nonn,more,hard AUTHOR Robert Price, Nov 21 2017 EXTENSIONS a(22) from Robert Price, Jul 16 2018 STATUS approved

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Last modified May 27 17:53 EDT 2020. Contains 334664 sequences. (Running on oeis4.)