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 A103109 Numbers n such that 9*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 1, 3, 4, 6, 9, 12, 16, 34, 129, 243, 252, 529, 4885, 6363, 12951, 13188, 29931, 34888, 49516, 67431, 77781 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (89*10^n-17)/9 is prime. a(22) > 10^5. - Robert Price, Nov 14 2015 LINKS Table of n, a(n) for n=1..21. Makoto Kamada, Prime numbers of the form 988...887. Index entries for primes involving repunits. FORMULA a(n) = A101018(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(89*10^n - 17)/9], Print[n]], {n, 0, 10000}] PROG (PARI) is(n)=isprime(9*10^n + 8*(10^n-1)/9 - 1) \\ Anders Hellström, Nov 14 2015 CROSSREFS Cf. A002275, A101018. Sequence in context: A202171 A182531 A097922 * A241639 A241655 A288346 Adjacent sequences: A103106 A103107 A103108 * A103110 A103111 A103112 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 19 2005 EXTENSIONS a(15)-a(18) from Kamada data by Robert Price, Dec 14 2010 a(19) from Erik Branger May 01 2013 by Ray Chandler, Aug 17 2013 a(20)-a(21) from Robert Price, Nov 14 2015 STATUS approved

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Last modified March 2 05:08 EST 2024. Contains 370460 sequences. (Running on oeis4.)