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A092396
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Smarandacheials for k=2.
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7
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OFFSET
| 0,1
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COMMENTS
| A generalization of double factorials: back and forth (1972).
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REFERENCES
| 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
| J. Dezert, Smarandacheials
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FORMULA
| 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
| !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
| Cf. A001818.
Sequence in context: A171671 A016886 A099761 * A018201 A181888 A000444
Adjacent sequences: A092393 A092394 A092395 * A092397 A092398 A092399
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KEYWORD
| sign
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AUTHOR
| J. Dezert (Jean.Dezert(AT)onera.fr), Mar 21 2004
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