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 A296059 Numbers k such that (10^k/8 + 1)/9 is prime. 0
 4, 7, 16, 43, 58, 106, 160, 229, 628, 1579, 3805, 16153, 31420 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Equivalently, numbers k such that (10^k + 8)/72 is prime. a(12) > 15000. - Robert G. Wilson v, Dec 09 2017 a(14) > 10^5. - Robert Price, Apr 24 2018 LINKS Table of n, a(n) for n=1..13. EXAMPLE 139, 138889, and 138888888888889 are prime, so 4, 7, and 16 are in the sequence. MATHEMATICA Select[Range[2000], PrimeQ[(10^#/8 + 1)/9] &] (* Michael De Vlieger, Dec 06 2017 *) ParallelMap[ If[ PrimeQ[(10^#/8 +1)/9], #, Nothing] &, Range@ 10000] (* Robert G. Wilson v, Dec 08 2017 *) PROG (PARI) isok(k) = (k>2) && isprime((10^k/8 + 1)/9); \\ Michel Marcus, Dec 05 2017 CROSSREFS Cf. A296029. Sequence in context: A144916 A217289 A050357 * A132334 A289521 A097661 Adjacent sequences: A296056 A296057 A296058 * A296060 A296061 A296062 KEYWORD nonn,more AUTHOR Patrick A. Thomas, Dec 04 2017 EXTENSIONS a(8)-a(11) from Jon E. Schoenfield, Dec 04 2017 a(12)-a(13) from Robert Price, Apr 24 2018 STATUS approved

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Last modified December 10 22:38 EST 2023. Contains 367717 sequences. (Running on oeis4.)