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 A282281 Numbers k such that (107*10^k - 17)/9 is prime. 0
 2, 3, 8, 12, 24, 105, 140, 231, 234, 260, 294, 354, 602, 813, 1562, 2961, 3450, 5622, 8121, 9014, 23052, 38505, 41139, 63576 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For k>0, numbers such that the digits 11 followed by k-1 occurrences of the digit 8 followed by the digit 7 is prime (see Example section). a(25) > 10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 118w7. EXAMPLE 3 is in this sequence because (107*10^3 - 17)/9 = 11887 is prime. Initial terms and primes associated: a(1) = 2, 1187; a(2) = 3, 11887; a(3) = 8, 1188888887; a(4) = 12, 11888888888887; a(5) = 24, 11888888888888888888888887; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(107*10^# - 17)/9] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A218542 A194452 A242516 * A321175 A079980 A025080 Adjacent sequences:  A282278 A282279 A282280 * A282282 A282283 A282284 KEYWORD nonn,more,hard AUTHOR Robert Price, Feb 10 2017 STATUS approved

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Last modified March 22 10:07 EDT 2019. Contains 321421 sequences. (Running on oeis4.)