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Search: id:A118130
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| A118130 |
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Composite lucky numbers whose divisors are also lucky numbers. |
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+0
1
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| 9, 21, 49, 63, 93, 111, 129, 169, 201, 219, 237, 259, 489, 511, 553, 559, 579, 723, 777, 961, 993, 1057, 1101, 1147, 1263, 1369, 1389, 1533, 1659, 1731, 1737, 1839, 1857, 1893, 1963, 2019, 2217, 2317, 2479, 2649, 2899, 2923, 2973, 3027, 3031, 3133, 3261
(list; graph; listen)
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OFFSET
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1,1
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MATHEMATICA
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lst = Range[1, 3350, 2]; i = 2; While[i <= (len = Length@lst) && (k = lst[[i]]) <= len, lst = Drop[lst, {k, len, k}]; i++ ]; fQ[n_] := If[PrimeQ@n, False, Block[{d = Take[Divisors@n, {2, -2}], k = 1, lmt = DivisorSigma[0, n] - 1}, While[k < lmt && MemberQ[lst, d[[k]]], k++ ]; k == lmt]]; Select[ Rest@lst, fQ@# &]
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CROSSREFS
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Cf. A000959, A043772.
Sequence in context: A020190 A135187 A133762 this_sequence A144482 A134717 A127989
Adjacent sequences: A118127 A118128 A118129 this_sequence A118131 A118132 A118133
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KEYWORD
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nonn
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AUTHOR
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Robert G. Wilson v (rgwv(AT)rgwv.com), May 12 2006
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