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A048631
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Xfactorials - like factorials but use carryless GF(2)[ X ] polynomial multiplication.
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4
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1, 1, 2, 6, 24, 120, 272, 1904, 15232, 124800, 848640, 7507200, 39738368, 433441792, 2589116416, 30419859456, 486717751296, 8128101580800, 132557598294016, 1971862458400768, 30421253686034432, 512675443057623040
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OFFSET
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0,3
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COMMENTS
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In formula X stands for the multiplication in a ring of GF(2)[ X ] polynomials
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LINKS
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Table of n, a(n) for n=0..21.
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FORMULA
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a(0) = 1, a(n) = n X a(n-1) (see the Maple function Xfactorial given below).
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MAPLE
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Xfactorial := proc(n); if(0 = n) then RETURN(1); else RETURN(Xmult(n, Xfactorial(n-1))); fi; end;
Xmult := proc(n, m) option remember; if(0 = n) then RETURN(0); else RETURN(XORnos(((n mod 2)*m), Xmult(floor(n/2), m*2))); fi; end;
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CROSSREFS
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Cf. A000142, A048720, A048632, A061922.
Sequence in context: A083267 A130480 A000804 * A189852 A189564 A178010
Adjacent sequences: A048628 A048629 A048630 * A048632 A048633 A048634
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KEYWORD
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easy,nonn
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AUTHOR
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Antti Karttunen
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STATUS
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approved
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