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A089017
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n for which the number consisting of a string of n 3's and a terminal 1 is not prime.
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3
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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
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listen;
history;
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internal format)
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OFFSET
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1,1
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COMMENTS
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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.
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LINKS
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MATHEMATICA
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Select[Range[2, 90], !PrimeQ[FromDigits[PadLeft[{1}, #, 3]]]&]-1 (* Harvey P. Dale, Jun 19 2012 *)
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PROG
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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STATUS
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approved
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