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 A271924 Denominator of (1/3)*(Product_{j=0..n-1} (((2*j+1)*(3*j+4))/((j+1)*(6*j+1))) - 1). 2
 1, 3, 13, 19, 285, 465, 17205, 147963, 345247, 11137, 291153, 175741, 12829093, 494964309, 494964309, 919219431, 6858791139, 706455487317, 77003648117553, 1262354887173, 1262354887173, 26321041453443, 500099787615417, 952244801075931, 50118147425049, 95795446344081 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS J. de Gier, Loops, matchings and alternating-sign matrices, arXiv:math.CO/0211285, 2002. EXAMPLE 1, 5/3, 29/13, 52/19, 913/285, 1693/465, 69769/17205, 658529/147963, 1667651/ 345247, 57873/11137, 1616141/291153, 1035959/175741, 79918969/12829093, ... MAPLE f3:=proc(n) local j; (1/3)*(mul(((2*j+1)*(3*j+4))/((j+1)*(6*j+1)), j=0..n-1)-1); end; t3:=[seq(f3(n), n=1..50)]; map(numer, t3); map(denom, t3); MATHEMATICA a[n_] := (1/3)*(Product[((2*j + 1)*(3*j + 4))/((j + 1)*(6*j + 1)), {j, 0, n - 1}] - 1) // Denominator; Array[a, 26] (* Jean-François Alcover, Nov 30 2017 *) CROSSREFS Sequences of fractions from de Gier paper: A271919-A271926. Sequence in context: A281998 A294676 A293465 * A178712 A273686 A215567 Adjacent sequences:  A271921 A271922 A271923 * A271925 A271926 A271927 KEYWORD nonn,frac AUTHOR N. J. A. Sloane, May 04 2016 STATUS approved

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Last modified April 18 05:11 EDT 2021. Contains 343072 sequences. (Running on oeis4.)