OFFSET
0,3
COMMENTS
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.
It appears that a(n) = A091440(n) for n >= 13. - Daniel Suteu, Sep 03 2019
LINKS
Achim Flammenkamp, The Multiply Perfect Numbers Page.
Fred Helenius, Multiperfect numbers.
FORMULA
a(n) = Min{w | floor(sigma(w!)/w!) = n}.
EXAMPLE
floor(sigma(842!)/842!) = 11 while floor(sigma(843!)/843!) = 12.
PROG
(PARI) a(n)=if(n<0, 0, s=1; while(sigma(s!)<n*s!, s++); s)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Labos Elemer, May 17 2001
EXTENSIONS
More terms from David Wasserman, Jun 18 2002
a(1) inserted and a(21)-a(30) added by Daniel Suteu, Sep 03 2019
STATUS
approved