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Search: id:A092396
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| A092396 |
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Smarandacheials for k=2. |
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+0
8
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| 9, 64, -225, -2304, 11025, 147456, -893025, -14745600, 108056025, 2123366400
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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A generalization of double factorials: back and forth (1972).
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REFERENCES
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J. Dezert, editor, Smarandacheials, Mathematics Magazine, Aurora, Canada, No. 4/2004 (to appear).
F. Smarandache, Back and Forth Factorials, Arizona State Univ., Special Collections, 1972.
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LINKS
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J. Dezert, Smarandacheials
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FORMULA
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a(n) = !n!_2 = Prod_{i=0, 1, 2, ... .}_{0<|n-2i|<=n}(n-2i) = n(n-2)(n-4)... = (-1)^(Int(n+1)/2) * (n!!)^2
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EXAMPLE
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!3!_2 = 3(3-2)(3-4)(3-6) = 9 and !4!_2 = 4(4-2)(4-6)(4-8) = 64.
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CROSSREFS
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Cf. A001818.
Sequence in context: A050792 A016886 A099761 this_sequence A018201 A000444 A143631
Adjacent sequences: A092393 A092394 A092395 this_sequence A092397 A092398 A092399
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KEYWORD
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sign
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AUTHOR
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J. Dezert (Jean.Dezert(AT)onera.fr), Mar 21 2004
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