OFFSET
1,2
LINKS
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
KEYWORD
nonn,frac
AUTHOR
N. J. A. Sloane, May 04 2016
STATUS
approved