A271919 - OEIS

A271919

Numerator of Product_{j=1..n-1} ((3*j+1)/(3*j+2)).

1, 4, 7, 7, 13, 104, 494, 988, 190, 5320, 20615, 589, 1147, 11470, 246605, 246605, 2416729, 62834954, 4488211, 4488211, 8831641, 10869712, 182067676, 2548947464, 2514502228, 27300309904, 134795280151, 269590560302, 3134773957, 25078191656, 570528860174, 60055669492, 59442856538

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..33.

J. de Gier, Loops, matchings and alternating-sign matrices, arXiv:math/0211285 [math.CO], 2002-2003.

EXAMPLE

1, 4/5, 7/10, 7/11, 13/22, 104/187, 494/935, 988/1955, 190/391, 5320/11339, 20615/45356, 589/1334, 1147/2668, 11470/27347, ...

MAPLE

f:=proc(n) local j;

mul(((3*j+1)/(3*j+2)), j=1..n-1); end;

t1:=[seq(f(n), n=1..50)];

map(numer, t1);

map(denom, t1);

MATHEMATICA

a[n_] := Product[(3j + 1)/(3j + 2), {j, 1, n - 1}] // Numerator;

Array[a, 33] (* Jean-François Alcover, Nov 17 2017 *)

PROG

(PARI) a(n) = numerator(prod(j=1, n-1, ((3*j+1)/(3*j+2)))); \\ Michel Marcus, Nov 17 2017

CROSSREFS

Sequences of fractions from de Gier paper: A271919-A271926.

Sequence in context: A063194 A071529 A349537 * A201125 A154922 A060409

Adjacent sequences: A271916 A271917 A271918 * A271920 A271921 A271922

KEYWORD

nonn,frac

AUTHOR

N. J. A. Sloane, May 04 2016

STATUS

approved