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Search: id:A122649
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| A122649 |
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Difference between the double factorial of the n-th nonnegative odd number and the double factorial of the n-th nonnegative even number. |
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+0
2
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| 0, 1, 7, 57, 561, 6555, 89055, 1381905, 24137505, 468934515, 10033419375, 234484536825, 5943863027025, 162446292283275, 4761954230608575, 149048910271886625, 4961463912662882625, 175022432901300859875
(list; graph; listen)
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OFFSET
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1,3
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FORMULA
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a(2*n+1) = (2*n+1)!! - (2*n)!!
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EXAMPLE
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a(1)=0, since 1!! - 0!! = 1 - 1 = 0, where the usual convention 0!! = 1 has been heeded. Note that 1 is the first nonnegative odd, and 0 the first nonnegative even number.
a(4)=57, since 7!! - 6!! = 1*3*5*7 - 6*4*2*1 = 105 - 48 = 57.
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MAPLE
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for n from 1 to 24 do: l[n]:=product(2*k-1, k=1..n); od: r[1]:=1; for n from 2 to 24 do: r[n]:=product(2*k, k=1..n-1); od; for k from 1 to 24 do: a[k]:=l[k]-r[k]; od;
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CROSSREFS
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Cf. A006882, A000165.
Adjacent sequences: A122646 A122647 A122648 this_sequence A122650 A122651 A122652
Sequence in context: A082413 A142990 A062192 this_sequence A051846 A051816 A015566
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KEYWORD
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easy,nonn
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AUTHOR
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Peter C. Heinig (algorithms(AT)gmx.de), Sep 21 2006
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