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

1,2

Comments

Appears to be an integer for n >= 1.

Links

Table of n, a(n) for n=1..24.

Formula

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

Mathematica

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

Prog

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

Crossrefs

Cf. A000005, A002866, A066843.

Sequence in context: A147889 A345246 A137858 * A374826 A204436 A135068

Adjacent sequences: A074737 A074738 A074739 * A074741 A074742 A074743

Keyword

easy,nonn

Author

Benoit Cloitre, Sep 05 2002

Status

approved