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 A283246 Numbers k such that (17*10^k - 179)/9 is prime. 0
 4, 5, 10, 13, 16, 106, 130, 148, 880, 1261, 2560, 2629, 3730, 5284, 7411, 8255, 9091, 9490, 10171, 14033, 25618, 39382, 47452 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For k > 1, numbers k such that the digit 1 followed by k-2 occurrences of the digit 8 followed by the digits 69 is prime (see Example section). a(24) > 2*10^5. LINKS Table of n, a(n) for n=1..23. Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 18w69. EXAMPLE 5 is in this sequence because (17*10^5 - 179)/9 = 188869 is prime. Initial terms and associated primes: a(1) = 4, 18869; a(2) = 5, 188869; a(3) = 10, 18888888869; a(4) = 13, 18888888888869; a(5) = 16, 18888888888888869; etc. MATHEMATICA Select[Range[2, 100000], PrimeQ[(17*10^# - 179)/9] &] PROG (PARI) is(n)=isprime((17*10^k - 179)/9) \\ Charles R Greathouse IV, Mar 05 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A222353 A094415 A114517 * A236283 A357865 A366864 Adjacent sequences: A283243 A283244 A283245 * A283247 A283248 A283249 KEYWORD nonn,more,hard,changed AUTHOR Robert Price, Mar 05 2017 STATUS approved

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Last modified June 21 03:48 EDT 2024. Contains 373535 sequences. (Running on oeis4.)