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A065581
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Smallest prime ending in exactly n 7's.
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6
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7, 277, 1777, 47777, 2477777, 16777777, 137777777, 577777777, 1777777777, 67777777777, 377777777777, 16777777777777, 17777777777777, 577777777777777, 2777777777777777, 157777777777777777
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OFFSET
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1,1
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LINKS
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Harry J. Smith, Table of n, a(n) for n=1,...,100
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MATHEMATICA
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Do[a = Table[7, {n} ]; k = 0; While[ b = FromDigits[ Join[ IntegerDigits[k], a]]; Mod[k, 10] == 7 || !PrimeQ[b], k++ ]; Print[b], {n, 1, 17} ]
k7[n_]:=Module[{c=FromDigits[PadRight[{}, n, 7]], k=0}, While[!PrimeQ[ k*10^n+ c], k++]; k*10^n+c]; Array[k7, 20] (* Harvey P. Dale, Jan 29 2013 *)
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PROG
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(PARI) { for (n=1, 100, t=10^n; b=7*(t - 1) / 9; d=0; while(!isprime(b + t*d), d++; if (d%10==7, d++)); write("b065581.txt", n, " ", b + t*d) ) } [From Harry J. Smith, Oct 23 2009]
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CROSSREFS
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Cf. A037067, A065590, A065821, A065580, A065582.
Sequence in context: A066413 A222942 A037067 * A062646 A009503 A209889
Adjacent sequences: A065578 A065579 A065580 * A065582 A065583 A065584
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KEYWORD
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nonn,base
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AUTHOR
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Robert G. Wilson v, Nov 28 2001
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STATUS
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approved
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