A025549 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,5

LINKS

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

FORMULA

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

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 *)

PROG

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

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).

Sequence in context: A346909 A369232 A369014 * A124013 A135584 A174538

Adjacent sequences: A025546 A025547 A025548 * A025550 A025551 A025552

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling

EXTENSIONS

Description corrected and sequence extended by Erich Friedman

More terms from Michel Marcus, Dec 02 2014

STATUS

approved

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