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 A056662 Numbers n such that 90*R_n + 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 3
 0, 1, 2, 16, 139, 989, 1886, 3529, 5995, 13819, 21872, 26044, 87719, 232598 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Also numbers n such that 10^(n+1) - 3 is a prime number. LINKS Makoto Kamada, Prime numbers of the form 99...997. FORMULA a(n) = A089675(n) - 1. - Robert Price, Nov 01 2014 MATHEMATICA Do[ If[ PrimeQ[ 90*(10^n - 1)/9 + 7 ], Print[n]], {n, 0, 1250}] CROSSREFS Cf. A002275, A089675. Sequence in context: A001252 A067058 A002302 * A151402 A199565 A003768 Adjacent sequences:  A056659 A056660 A056661 * A056663 A056664 A056665 KEYWORD hard,nonn AUTHOR Robert G. Wilson v, Aug 09 2000 EXTENSIONS More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 a(13)-a(14) derived from A089675 by Robert Price, Nov 01 2014 STATUS approved

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Last modified June 22 03:25 EDT 2021. Contains 345367 sequences. (Running on oeis4.)