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A268218
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a(n) = (n!/3!)*Sum(1/k!,k=1..n-3).
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3
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0, 0, 0, 0, 4, 30, 200, 1435, 11536, 103908, 1039200, 11431365, 137176600, 1783296086, 24966145568, 374492183975, 5991874944160, 101861874051400, 1833513732926016, 34836760925595273, 696735218511906600, 14631439588750039930, 321891670952500880000, 7403508431907520241771
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OFFSET
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0,5
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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(3);
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PROG
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(PARI) a(n) = (n!/3!)*sum(k=1, n-3, 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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