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 A259134 Numbers k such that 9*R_k + 7*10^k - 2 is prime, where R_k = 11...11 is the repunit (A002275) of length k. 0
 0, 2, 4, 28, 156, 322, 352, 1212, 1284, 7984, 15192, 84772, 119930, 148860 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also, numbers k such that 8*10^k - 3 is prime. Terms from Kamada data. Note that Kamada does not recognize k=0 as 5 is a degenerate case of form ABB..BBA. a(15) > 2*10^5. LINKS Makoto Kamada, Near-repdigit numbers of the form ABB...BBA. Makoto Kamada, Prime numbers of the form 799...997. EXAMPLE For k=2, 9*R_2 + 7*10^k - 2 = 99 + 700 - 2 = 797 which is prime. MATHEMATICA Select[Range[0, 200000], PrimeQ[8*10^#-3] &] CROSSREFS Cf. A002275. Sequence in context: A264667 A356700 A357158 * A117443 A095858 A062792 Adjacent sequences: A259131 A259132 A259133 * A259135 A259136 A259137 KEYWORD nonn,more,hard AUTHOR Robert Price, Jun 18 2015 STATUS approved

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Last modified December 7 14:31 EST 2022. Contains 358656 sequences. (Running on oeis4.)