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 A286426 Numbers k such that (22*10^k + 71)/3 is prime. 0
 0, 1, 2, 6, 20, 23, 86, 146, 167, 340, 472, 500, 898, 907, 936, 1133, 2069, 3166, 4207, 5275, 9700, 20407, 28009, 32923, 53264 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 3 followed by the digits 57 is prime (see Example section). a(26) > 2*10^5. LINKS Table of n, a(n) for n=1..25. Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 73w57. EXAMPLE 2 is in this sequence because (22*10^2 + 71)/3 = 757 is prime. Initial terms and associated primes: a(1) = 0, 31; a(2) = 1, 97; a(3) = 2, 757; a(4) = 6, 7333357; a(5) = 20, 733333333333333333357; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(22*10^# + 71)/3] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A205012 A254120 A356778 * A028689 A156269 A370974 Adjacent sequences: A286423 A286424 A286425 * A286427 A286428 A286429 KEYWORD nonn,more,hard,changed AUTHOR Robert Price, May 09 2017 STATUS approved

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Last modified June 14 10:58 EDT 2024. Contains 373396 sequences. (Running on oeis4.)