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 A294569 Numbers k such that (43*10^k + 101)/9 is prime. 0
 1, 3, 6, 9, 12, 27, 33, 45, 63, 81, 351, 357, 540, 582, 1998, 2401, 4140, 4675, 6963, 7873, 19749, 138648, 173826, 190351 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k > 1, numbers such that the digit 4 followed by k-2 occurrences of the digit 7 followed by the digits 89 is prime (see Example section). a(25) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 47w89 EXAMPLE 3 is in this sequence because (43*10^3 + 101)/9 = 4789 is prime. Initial terms and primes associated: a(1) = 1, 59; a(2) = 3, 4789; a(3) = 6, 4777789; a(4) = 9, 4777777789; a(5) = 12, 4777777777789; etc. MATHEMATICA Select[Range[1, 100000], PrimeQ[(43*10^# + 101)/9] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A118519 A282762 A089757 * A277250 A083491 A086423 Adjacent sequences:  A294566 A294567 A294568 * A294570 A294571 A294572 KEYWORD nonn,more,hard AUTHOR Robert Price, Nov 02 2017 EXTENSIONS a(22)-a(24) from Robert Price, Nov 30 2018 STATUS approved

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Last modified December 9 17:18 EST 2019. Contains 329879 sequences. (Running on oeis4.)