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 A284595 Numbers k such that (349*10^k - 7)/9 is prime. 0
 2, 12, 21, 30, 63, 86, 140, 173, 308, 318, 402, 410, 441, 492, 2186, 4580, 5100, 5208, 5810, 7476, 21677, 31766, 45357, 48036, 66720 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For k > 1, numbers k such that the digits 38 followed by k occurrences of the digit 7 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 387w. EXAMPLE 2 is in this sequence because (349*10^2 - 7)/9 = 3877 is prime. Initial terms and associated primes: a(1) = 2, 3877; a(2) = 12, 38777777777777; a(3) = 21, 38777777777777777777777; a(4) = 30, 38777777777777777777777777777777; a(5) = 63, 38777777777777777777777777777777777777777777777777777777777777777; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(349*10^# - 7)/9] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A304813 A279424 A073041 * A053898 A058413 A053890 Adjacent sequences: A284592 A284593 A284594 * A284596 A284597 A284598 KEYWORD nonn,more,hard AUTHOR Robert Price, Mar 29 2017 STATUS approved

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Last modified July 15 11:01 EDT 2024. Contains 374332 sequences. (Running on oeis4.)