OFFSET
1,2
COMMENTS
EXAMPLE
a(4) = 5 because 5 products of distinct factorials do not exceed 4!, namely, 1, 2, 6, 12 and 24.
MATHEMATICA
d[k_] := (m=1; With[{p=With[{s=Subsets[Table[n!, {n, k}]]}, Sort[Table[Apply[Times, s[[n]]], {n, Length[s]}]]]}, While[p[[m]]<=k!, m++ ]; Length[Union[Take[p, m-1]]]]); Table[d[k], {k, 19}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonathan Sondow, Dec 22 2004
EXTENSIONS
a(20)-a(48) from Donovan Johnson, May 30 2012
STATUS
approved