OFFSET
1,3
COMMENTS
LINKS
FORMULA
a(n) = floor(n-(n-1)^n/n^(n-1)).
EXAMPLE
a(1) = 1 because the image of a function from [1] to [1] has one value. a(2) = 1 since we can consider functions with domain {x,y}, and image {X,Y}. We can have f(x)=X, f(y)=X; f(x)=X, f(y)=Y; f(x)=Y, f(y)=Y; f(x)=Y, f(y)=X.
The sum of the cardinalities of the images divided by the number of functions is (1+2+1+2)/4 = 1.5. Floor(1.5)=1.
CROSSREFS
KEYWORD
nonn
AUTHOR
Washington Bomfim, Mar 05 2012
STATUS
approved