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 A296094 Numbers k such that (43*10^k + 47)/9 is prime. 0
 1, 3, 7, 12, 15, 21, 85, 177, 204, 477, 487, 1686, 2179, 2815, 2892, 3466, 7308, 17883, 25431, 69048, 89169, 126441 (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 83 is prime (see Example section). a(23) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 47w83 EXAMPLE 3 is in this sequence because (43*10^3 + 47)/9 = 4783 is prime. Initial terms and primes associated: a(1) = 1, 53; a(2) = 3, 4783; a(3) = 7, 47777783; a(4) = 12, 4777777777783; a(5) = 15, 4777777777777783; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(43*10^# + 47)/9] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A310234 A310235 A310236 * A075895 A033015 A225574 Adjacent sequences:  A296091 A296092 A296093 * A296095 A296096 A296097 KEYWORD nonn,more,hard AUTHOR Robert Price, Dec 04 2017 EXTENSIONS a(22) from Robert Price, Dec 01 2018 STATUS approved

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Last modified December 10 20:23 EST 2019. Contains 329909 sequences. (Running on oeis4.)