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A220092
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a(n) = ((2*n-1)!! + (-1)^((n-1)*(n-2)/2))/2.
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1
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1, 2, 7, 52, 473, 5198, 67567, 1013512, 17229713, 327364538, 6874655287, 158117071612, 3952926790313, 106729023338438, 3095141676814687, 95949391981255312, 3166329935381425313, 110821547738349885938, 4100397266318945779687, 159915493386438885407812
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OFFSET
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1,2
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COMMENTS
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Described by V. Shevelev as an instance of a fast-growing nontrivial sequence that is similar to the naturals in the sense that A007814(a(n)) = A007814(n).
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LINKS
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PROG
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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