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A101609
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a(n) = n! * Sum_{k=1..floor(n/2)} 1/k.
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4
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0, 2, 6, 36, 180, 1320, 9240, 84000, 756000, 8285760, 91143360, 1173553920, 15256200960, 226040855040, 3390612825600, 56865153945600, 966707617075200, 18112111963545600, 344130127307366400, 7125892746964992000
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OFFSET
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1,2
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LINKS
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FORMULA
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a(1) = 0, a(n) = a(n-1)*n + (1 + (-1)^n)*(n-1)!. - Daniel Suteu, Feb 06 2017
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MATHEMATICA
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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