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 A056654 Numbers n such that 10*R_n + 3 is prime, where R_n is the repunit (A002275) of length n. 507
 0, 1, 2, 4, 8, 10, 23, 83, 220, 1313, 2951, 20015, 51053 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Also numbers n such that (10^(n+1)+17)/9 is prime. a(14) > 10^5. - Robert Price, Nov 01 2014 LINKS Makoto Kamada, Prime numbers of the form 11...113. FORMULA a(n) = A097683(n+1) - 1. - Robert Price, Nov 01 2014 EXAMPLE 8 is a term because 111111113 is a prime. MATHEMATICA Do[ m = n; If[ primeQ[ 10*(10^n - 1)/9 + 3 ], Print[ n ] ], {n, 1, 1350} ] CROSSREFS Cf. A093011 (corresponding primes), A097683. Sequence in context: A127101 A308832 A124849 * A020950 A056386 A331027 Adjacent sequences:  A056651 A056652 A056653 * A056655 A056656 A056657 KEYWORD hard,nonn AUTHOR Robert G. Wilson v, Aug 09 2000 EXTENSIONS a(11) (only a probable prime) from Rick L. Shepherd, Mar 14 2004 a(12)-a(13) derived from A097683 by Robert Price, Nov 01 2014 STATUS approved

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Last modified January 27 17:58 EST 2020. Contains 331296 sequences. (Running on oeis4.)