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 A089017 n for which the number consisting of a string of n 3's and a terminal 1 is not prime. 3
 8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 40, 41, 42, 43, 44, 45, 46, 47, 48, 50, 51, 52, 53, 54, 55, 56, 57, 58, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 78, 79, 80, 81, 82 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Complement of A055520(n)=A055557(n) - 1. The first n for which {10^(n+1) - 7}/3 is composite is thus n=8,corresponding to 333333331=17*19607843. LINKS MATHEMATICA Select[Range[2, 90], !PrimeQ[FromDigits[PadLeft[{1}, #, 3]]]&]-1 (* Harvey P. Dale, Jun 19 2012 *) PROG (PARI) is(n)=ispseudoprime((10^(n+1)-7)/3) \\ Charles R Greathouse IV, Oct 23 2013 CROSSREFS Cf. A055520, A089018. Sequence in context: A168098 A020722 A046037 * A182361 A023391 A115419 Adjacent sequences:  A089014 A089015 A089016 * A089018 A089019 A089020 KEYWORD base,nonn AUTHOR Lekraj Beedassy, Nov 04 2003 STATUS approved

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Last modified July 18 19:00 EDT 2019. Contains 325144 sequences. (Running on oeis4.)