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A061556
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a(n) is the least k > 0 such that sigma(k!) >= n*k!.
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2
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1, 1, 3, 5, 9, 14, 23, 43, 79, 149, 263, 461, 823, 1451, 2549, 4483, 7879, 13859, 24247, 42683, 75037, 131707, 230773, 405401, 710569, 1246379, 2185021, 3831913, 6720059, 11781551, 20657677
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OFFSET
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0,3
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COMMENTS
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It seems that, for n > 1, a(n+1) < 2*a(n). Does lim_{n -> infinity} a(n+1)/a(n) = 2? - Benoit Cloitre, Aug 18 2002
Smallest number m such that the abundancy-index of m! is at least n.
Floor(sigma(m!)/m!) = n; note that abundancy-index [= sigma(u)/u] here is not necessarily an integer.
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LINKS
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FORMULA
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a(n) = Min{w | floor(sigma(w!)/w!) = n}.
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EXAMPLE
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floor(sigma(842!)/842!) = 11 while floor(sigma(843!)/843!) = 12.
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PROG
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(PARI) a(n)=if(n<0, 0, s=1; while(sigma(s!)<n*s!, s++); s)
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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a(1) inserted and a(21)-a(30) added by Daniel Suteu, Sep 03 2019
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STATUS
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approved
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