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A372509
Numbers that can be written as a product of double factorials of odd numbers.
0
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
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
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, May 04 2024
STATUS
approved