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Search: id:A114796
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| 1, 1, 2, 6, 24, 120, 720, 5040, 80640, 2177280, 87091200, 4790016000, 344881152000, 31384184832000, 7030057402368000, 2847173247959040000, 1822190878693785600000, 1703748471578689536000000
(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, Multifactorial.
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FORMULA
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a(n) = Prod[i=0 to n] n!!!!!!. a(n) = Prod[i=0 to n] n!6. a(n) = Prod[i=0 to n] A085158(n). a(n) = n!!!!!! * a(n-1) where a(0) = 1, a(1) = 1 and n >= 2. a(n) = n*(n-6)!!!!!! * a(n-1) where a(0) = 1, a(1) = 1, a(2) = 2.
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EXAMPLE
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a(10) = 1!6 * 2!6 * 3!6 * 4!6 * 5!6 * 6!6 * 7!6 * 8!6 * 9!6 * 10!6
= 1 * 2 * 3 * 4 * 5 * 6 * 7 * 16 * 27 * 40 = 87091200 = 2^11 * 3^5 * 5^2 * 7.
Note that a(10) + 1 = 87091201 is prime, as is a(9) + 1 = 2177281.
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CROSSREFS
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Cf. A006882, A007662, A085150, A085157, A085158, A000178, A114347.
Adjacent sequences: A114793 A114794 A114795 this_sequence A114797 A114798 A114799
Sequence in context: A074166 A130641 A129655 this_sequence A114790 A079854 A024923
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost2(AT)yahoo.com), Feb 18 2006
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