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A003594
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Numbers of the form 3^i*7^j with i, j >= 0.
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8
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1, 3, 7, 9, 21, 27, 49, 63, 81, 147, 189, 243, 343, 441, 567, 729, 1029, 1323, 1701, 2187, 2401, 3087, 3969, 5103, 6561, 7203, 9261, 11907, 15309, 16807, 19683, 21609, 27783, 35721, 45927, 50421, 59049, 64827, 83349, 107163, 117649
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OFFSET
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1,2
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LINKS
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Table of n, a(n) for n=1..41.
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MATHEMATICA
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f[upto_]:=Sort[Select[Flatten[3^First[#] 7^Last[#] & /@ Tuples[{Range[0, Floor[Log[3, upto]]], Range[0, Floor[Log[7, upto]]]}]], # <= upto &]]; f[120000] (* From Harvey P. Dale, Mar 04 2011 *)
fQ[n_] := PowerMod[21, n, n] == 0; Select[Range[120000], fQ] (* Bruno Berselli, Sep 24 2012 *)
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PROG
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(PARI) list(lim)=my(v=List(), N); for(n=0, log(lim)\log(7), N=7^n; while(N<=lim, listput(v, N); N*=3)); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jun 28 2011
(MAGMA) [n: n in [1..120000] | PrimeDivisors(n) subset [3, 7]]; // Bruno Berselli, Sep 24 2012
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CROSSREFS
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Sequence in context: A056745 A057263 A057493 * A014854 A108729 A133027
Adjacent sequences: A003591 A003592 A003593 * A003595 A003596 A003597
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KEYWORD
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nonn,changed
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AUTHOR
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N. J. A. Sloane.
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STATUS
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approved
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