A072116 a(n) = (2n)!/(phi(2n)!)^2.

2, 6, 180, 70, 6300, 831600, 168168, 12870, 12350257920, 1496523600, 85357272, 381649434566400, 1757701400, 1328822258400, 163162002966958195200000, 601080390, 674412197580, 1621291929818474833920000, 12759640231800

Offset

1,1

Links

G. C. Greubel, Table of n, a(n) for n = 1..300

Maple

with(numtheory); seq((2*n)!/(phi(2*n)!)^2, n = 1..20); # G. C. Greubel, Aug 25 2019

Prog

(PARI) for(n=1, 30, print1((2*n)!/(eulerphi(2*n))!^2, ", "))
(Magma) F:=Factorial; [F(2*n)/F(EulerPhi(2*n))^2 : n in [1..20]]; // G. C. Greubel, Aug 25 2019
(Sage) f=factorial; [f(2*n)/f(euler_phi(2*n))^2 for n in (1..20)] # G. C. Greubel, Aug 25 2019
(GAP) F:=Factorial;; List([1..20], n-> F(2*n)/F(Phi(2*n))^2 ); # G. C. Greubel, Aug 25 2019

Crossrefs

Sequence in context: A135937 A182523 A137532 * A203430 A298883 A252740

Adjacent sequences: A072113 A072114 A072115 * A072117 A072118 A072119

Keyword

easy,nonn

Author

Benoit Cloitre, Jun 19 2002

Status

approved