Multifactorial
A generalization of the Factorial and Double Factorial,
 |  |  | |
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etc., where the product runs through positive integers. The Factorials
for 
, 2, ..., are 1,2, 6, 24, 120, 720, ... (Sloane's A000142); the Double Factorials 
are 1, 2, 3, 8, 15, 48,105, ... (Sloane's A006882); the triple factorials 
are 1, 2, 3, 4, 10, 18, 28, 80, 162, 280, ... (Sloane's A007661); andthe quadruple factorials 
are 1, 2, 3, 4, 5, 12, 21, 32, 45, 120, ... (Sloane's A007662).See also Factorial, Gamma Function
References
Sloane, N. J. A. SequencesA000142/M1675,A006882/M0876,A007661/M0596, andA007661/M0534in ``An On-Line Version of the Encyclopedia of Integer Sequences.''http://www.research.att.com/~njas/sequences/eisonline.html and Sloane, N. J. A. and Plouffe, S.The Encyclopedia of Integer Sequences. San Diego: Academic Press, 1995.
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