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A110371
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a(n)=[(n+1)(n+2)(n+3)...(2n)]/(1+2+3+...+n).
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1
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2, 4, 20, 168, 2016, 31680, 617760, 14414400, 392071680, 12189864960, 426645273600, 16606346803200, 711700577280000, 33307587016704000, 1690360041097728000, 92472637542405120000, 5425061402487767040000, 339780161524233830400000, 22629358757513973104640000
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OFFSET
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1,1
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COMMENTS
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LINKS
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Ron Knott, 2016, January 2016.
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FORMULA
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{2*(2n)!}/{(n+1)!*n}
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EXAMPLE
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a(4) = 5*6*7*8/10 = 168.
a(5) = 10*9*8*7*6/(5+4+3+2+1) = 2016.
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MAPLE
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MATHEMATICA
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Table[(Times@@Range[n+1, 2n])/((n(n+1))/2), {n, 20}] (* or *) Table[ 2(n-1)! CatalanNumber[n], {n, 20}] (* Harvey P. Dale, Jul 15 2016 *)
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PROG
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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