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 A259137 Numbers k such that 8*R_k + 7*10^k - 1 is prime, where R_k = 11...11 is the repunit (A002275) of length k. 0
 2, 4, 86, 112, 170, 566, 1688, 8902, 115810 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also, numbers k such that (71*10^k - 17)/9 is prime. Terms from Kamada data. LINKS Table of n, a(n) for n=1..9. Makoto Kamada, Near-repdigit numbers of the form ABB...BBA. Makoto Kamada, Prime numbers of the form 788...887. Index entries for primes involving repunits. EXAMPLE For k=2, 8*R_2 + 7*10^k - 1 = 88 + 700 - 1 = 787 which is prime. MATHEMATICA Select[Range[0, 100000], PrimeQ[(71*10^#-17)/9] &] PROG (Magma) [n: n in [0..300] | IsPrime((71*10^n-17)div 9)]; // Vincenzo Librandi, Jun 19 2015 CROSSREFS Cf. A002275. Sequence in context: A012435 A121103 A018397 * A009217 A015170 A013146 Adjacent sequences: A259134 A259135 A259136 * A259138 A259139 A259140 KEYWORD more,hard,nonn AUTHOR Robert Price, Jun 18 2015 STATUS approved

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Last modified December 5 03:04 EST 2023. Contains 367567 sequences. (Running on oeis4.)