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A093346
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Array read by antidiagonals: T(r,n) = number of two-stack sortable r-permutations.
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0
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1, 1, 2, 1, 3, 6, 1, 4, 15, 22, 1, 5, 28, 95, 91, 1, 6, 45, 252, 690, 408, 1, 7, 66, 525, 2618, 5481, 1938, 1, 8, 91, 946, 7095, 29848, 46376, 9614, 1, 9, 120, 1547, 15741, 105417, 363216, 411255, 49335, 1, 10, 153, 2360, 30576, 288288, 1673535, 4638348, 3781635, 260130
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OFFSET
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1,3
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LINKS
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FORMULA
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T(r,n) = 2(r+1) * ((2r+1)n)!/[n!*(2rn+2)! ].
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MATHEMATICA
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T[r_, n_] := 2(r+1) * ((2r+1)n)!/(n!*(2r n+2)!); Table[T[r-n+1, n], {r, 1, 10}, {n, 1, r}] // Flatten (* Jean-François Alcover, Feb 18 2019 *)
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PROG
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(PARI) T(r, n)=2*(r+1)*((2*r+1)*n)!/(n!*(2*r*n+2)!)
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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