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A268707
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Smallest n-digit prime having at least n-1 digits equal to 9.
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6
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2, 19, 199, 1999, 49999, 199999, 2999999, 19999999, 799999999, 9199999999, 59999999999, 959999999999, 9919999999999, 59999999999999, 499999999999999, 9299999999999999, 99919999999999999, 994999999999999999, 9991999999999999999, 29999999999999999999
(list;
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refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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LINKS
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Michel Lagneau, Michael De Vlieger and Robert G. Wilson v, Table of n, a(n) for n = 1..1225
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MATHEMATICA
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f[n_] := Block[{k = 0, p = {}, r = (10^n - 1), s = Range@ 10 - 10}, While[k < n - 0, AppendTo[p, Select[r + 10^k*s, PrimeQ]]; k++]; p = Min@ Flatten@ p]; Array[f, 20]
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PROG
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(PARI) a(n)=my(t=10^n-1, p); forstep(d=n-1, 0, -1, forstep(k=8, 1, -1, p=t-10^d*k; if(ispseudoprime(p), return(p)))); -1 \\ Charles R Greathouse IV, Mar 21 2016
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CROSSREFS
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Cf. A037071, A241100, A268702 - A268706, A241206, A266148.
Sequence in context: A218117 A145104 A114016 * A037071 A126039 A091852
Adjacent sequences: A268704 A268705 A268706 * A268708 A268709 A268710
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KEYWORD
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nonn,base
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AUTHOR
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Michel Lagneau, Michael De Vlieger and Robert G. Wilson v, Feb 11 2016
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STATUS
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approved
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