A271920 Denominator of Product_{j=1..n-1} ((3*j+1)/(3*j+2)).
1, 5, 10, 11, 22, 187, 935, 1955, 391, 11339, 45356, 1334, 2668, 27347, 601634, 614713, 6147130, 162898945, 11847196, 12051458, 24102916, 30128645, 512186965, 7273054903, 7273054903, 80003603933, 400018019665, 809792576395, 9526971487, 77081860213, 1772882784899, 188604551585, 188604551585
Offset: 1
Examples
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, ...
Links
- J. de Gier, Loops, matchings and alternating-sign matrices, arXiv:math.CO/0211285, 2002-2003.
Crossrefs
Programs
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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);
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Mathematica
Table[Product[(3*j+1)/(3*j+2), {j, 1, n-1}] // Denominator, {n, 1, 33}] (* Jean-François Alcover, Mar 25 2018 *) -
PARI
a(n) = denominator(prod(j=1, n-1, (3*j+1)/(3*j+2))); \\ Michel Marcus, Mar 25 2018