A025549 a(n) = (2n-1)!!/lcm{1,3,5,...,2n-1}.

1, 1, 1, 1, 3, 3, 3, 45, 45, 45, 945, 945, 4725, 42525, 42525, 42525, 1403325, 49116375, 49116375, 1915538625, 1915538625, 1915538625, 86199238125, 86199238125, 603394666875, 30773128010625, 30773128010625, 1692522040584375, 96473756313309375, 96473756313309375

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• easy

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..569

Crossrefs

Not always equal to the second left hand column of A161198 triangle divided by A074599. - Johannes W. Meijer, Jun 08 2009

Cf. A196274 (run lengths of equal terms).

Programs

Maple

seq(doublefactorial(2*n-1)/lcm(seq((2*k-1), k=1..n)), n=1..27) ; # Johannes W. Meijer, Jun 08 2009

Mathematica

L[ {x___} ] := LCM[ x ]; Table[ (2n-1)!!/L[ Range[ 1, 2n-1, 2 ] ], {n, 1, 50} ]
(* Second program: *)
Array[#!!/LCM @@ Range[1, #, 2] &[2 # - 1] &, 30] (* Michael De Vlieger, Feb 19 2019 *)

PARI

a(n) = (((2*n)!/n!)/2^n)/lcm(vector(n, i, 2*i-1)); \\ Michel Marcus, Dec 02 2014

Formula

a(n) = A001147(n)/A025547(n). - Michel Marcus, Dec 02 2014

Extensions

Description corrected and sequence extended by Erich Friedman

More terms from Michel Marcus, Dec 02 2014