A118130 Composite lucky numbers whose divisors are also lucky numbers.

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

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from T. D. Noe)

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: A160414 A256530 A363634 * A144482 A251212 A176896

Adjacent sequences: A118127 A118128 A118129 * A118131 A118132 A118133

Keyword

nonn

Author

Robert G. Wilson v, May 12 2006

Status

approved