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A118130 Composite lucky numbers whose divisors are also lucky numbers. 2
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; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

T. D. Noe, Table of n, a(n) for n=1..1000

MATHEMATICA

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@# &]

CROSSREFS

Cf. A000959, A043772.

Sequence in context: A133762 A160414 A256530 * A144482 A251212 A176896

Adjacent sequences:  A118127 A118128 A118129 * A118131 A118132 A118133

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, May 12 2006

STATUS

approved

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Last modified March 21 10:27 EDT 2019. Contains 321368 sequences. (Running on oeis4.)