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A000779
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a(n) = 2*(2n-1)!!-(n-1)!*2^(n-1), where (2n-1)!! is A001147(n).
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1
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1, 4, 22, 162, 1506, 16950, 224190, 3408930, 58596930, 1123663590, 23782729950, 550718680050, 13849716607650, 375904338960150, 10952237584237950, 340947694234397250, 11294123783425733250, 396665528378000631750
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OFFSET
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1,2
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LINKS
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MAPLE
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MATHEMATICA
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PROG
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(Magma) A001147:=func< n | n eq 0 select 1 else &*[ k: k in [1..2*n-1 by 2] ] >; [ 2*A001147(n)-Factorial(n-1)*2^(n-1): n in [1..20] ]; // Klaus Brockhaus, Jun 22 2011
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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