A074740 a(n) = n!*2^(n-1)/Product_{k=1..n} tau(k) where tau = A000005.

1, 2, 6, 16, 80, 240, 1680, 6720, 40320, 201600, 2217600, 8870400, 115315200, 807206400, 6054048000, 38745907200, 658680422400, 3952082534400, 75089568153600, 500597121024000, 5256269770752000, 57818967478272000, 1329836252000256000, 7979017512001536000

Offset: 1

Author

Benoit Cloitre, Sep 05 2002

Keywords

• easy
• nonn

Comments

Appears to be an integer for n >= 1.

Crossrefs

Cf. A000005, A002866, A066843.

Programs

Mathematica

FoldList[Times, Array[2*#/DivisorSigma[0, #]&, 24]] / 2 (* Amiram Eldar, May 04 2025 *)

PARI

a(n) = n!*2^(n-1)/prod(k=1, n, numdiv(k)); \\ Michel Marcus, Jan 09 2021

Formula

a(n) = A002866(n) / A066843(n). - Michel Marcus, Jan 09 2021 [Corrected by Georg Fischer, Dec 13 2022]