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A070740
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Order of the subgroup of the symmetric group S_(2n) generated by the 2 cycles: (1,2,...n,2n,2n-1,...,n+1) and (1,2,...,2n).
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1
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24, 36, 40320, 7200, 479001600, 25401600, 20922789888000, 65840947200, 2432902008176640000, 1593350922240000, 620448401733239439360000, 19387894021816320000, 304888344611713860501504000000, 1710012252724199424000000, 263130836933693530167218012160000000
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OFFSET
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2,1
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LINKS
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FORMULA
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If n is even: a(n) = (2n)!.
If n is congruent to 1 mod 4: a(n) = (n!)^2 / 2.
If n is congruent to 3 mod 4: a(n) = (n!)^2.
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PROG
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(PARI) a(n) = if(n < 2, 0, if(n%2==0, (2*n)!, (n!)^2 / if(n%4==1, 2, 1))); \\ Andrew Howroyd, Jul 04 2018
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Sharon Sela (sharonsela(AT)hotmail.com), May 14 2002
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EXTENSIONS
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STATUS
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approved
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