A372509 Numbers that can be written as a product of double factorials of odd numbers.

1, 3, 9, 15, 27, 45, 81, 105, 135, 225, 243, 315, 405, 675, 729, 945, 1215, 1575, 2025, 2187, 2835, 3375, 3645, 4725, 6075, 6561, 8505, 10125, 10395, 10935, 11025, 14175, 18225, 19683, 23625, 25515, 30375, 31185, 32805, 33075, 42525, 50625

Offset

1,2

Links

Table of n, a(n) for n=1..42.

Mathematica

kmax = 60000;
maxExponent = 10;
ff = Select[TakeWhile[Range[3, kmax], #!! < kmax &]!!, OddQ];
lg = Length@ff;
iter = Sequence @@ Table[{x[i], 0, maxExponent}, {i, 1, lg}];
seq = Table[k = Times @@ Table[ff[[i]]^x[i] , {i, 1, lg}]; If[k <= kmax, k, Nothing], Evaluate@iter] // Flatten // Union (* Jean-François Alcover, May 11 2024 *)

Crossrefs

Cf. A001013, A001147, A025487, A057863.

Sequence in context: A363523 A339886 A147516 * A233819 A131822 A131801

Adjacent sequences: A372506 A372507 A372508 * A372510 A372511 A372512

Keyword

nonn

Author

Ilya Gutkovskiy, May 04 2024

Status

approved