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A268219
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a(n) = (n!/4!)*Sum(1/k!,k=1..n-4).
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4
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0, 0, 0, 0, 0, 5, 45, 350, 2870, 25956, 259770, 2857800, 34294095, 445823950, 6241536301, 93623045880, 1497968735900, 25465468512680, 458378433231300, 8709190231398576, 174183804627976365, 3657859897187509650, 80472917738125219615, 1850877107976880060000, 44421050591445121450626
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OFFSET
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0,6
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LINKS
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MAPLE
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g:=(r, n)->(n!/r!)*add(1/k!, k=1..n-r);
g2:=r->[seq(g(r, n), n=0..30)];
g2(4);
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PROG
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(PARI) a(n) = (n!/4!)*sum(k=1, n-4, 1/k!); \\ Michel Marcus, Jan 30 2016
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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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