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Search: id:A113296
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| 1, 1, 2, 6, 48, 720, 34560, 3628800, 1393459200, 1316818944000, 5056584744960000, 52563198423859200000, 2422112183371431936000000, 327312129899898454671360000000, 211155601241022491077587763200000000
(list; graph; listen)
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OFFSET
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0,3
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LINKS
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Eric Weisstein's World of Mathematics, Double Factorial.
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FORMULA
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a(n) = Prod[i=0 to n] n!!. a(n) = n!! * a(n-1) where a(0) = 0, a(1) = 1 and n >= 2. a(n) = n*(n-2)!! * a(n-1) where a(0) = 0, a(1) = 1 and n >= 2.
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EXAMPLE
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a(10) = 1!! * 2!! * 3!! * 4!! * 5!! * 6!! * 7!! * 8!! * 9!! * 10!!
= 1 * 2 * 3 * 8 * 15 * 48 * 105 * 384 * 945 * 3840
= 5056584744960000 = 2^23 x 3^9 x 5^4 x 7^2.
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CROSSREFS
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Cf. A006882.
Sequence in context: A052717 A129464 A003053 this_sequence A063744 A141609 A096313
Adjacent sequences: A113293 A113294 A113295 this_sequence A113297 A113298 A113299
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), Feb 18 2006
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