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A077539
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a(n) = floor(T(n+1)!*T(n-1)!/(T(n)!)^2), where T(n) = n(n+1)/2 = the n-th triangular number.
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0
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6, 20, 42, 71, 108, 152, 204, 263, 330, 403, 485, 573, 669, 773, 884, 1002, 1128, 1261, 1401, 1549, 1704, 1866, 2036, 2214, 2398, 2591, 2790, 2997, 3211, 3433, 3662, 3898, 4142, 4394, 4652, 4918, 5192, 5472, 5761, 6056, 6359, 6669, 6987
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OFFSET
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1,1
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COMMENTS
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The ratio itself is an integer only for n = 1, 2 and 3.
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LINKS
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EXAMPLE
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a(1) = 6 = (2*3)/1;
a(2) = 20 = (4*5*6)/(2*3), etc.
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MATHEMATICA
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Floor[(#[[1]]!*#[[3]]!)/(#[[2]]!)^2]&/@Partition[Accumulate[ Range[ 0, 50]], 3, 1] (* Harvey P. Dale, Aug 21 2015 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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More terms from Mark Hudson (mrmarkhudson(AT)hotmail.com), Feb 11 2003
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STATUS
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approved
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