17# sin_cera
f(n)=[(n!+1)/e] for n>0, f(n)=[n!/e+1/n] for n>1 and f(n)=[(e+1/e).n! ]-[e.n! ] for n>1; where [x] denotes the floor of x. - Mehdi Hassani (mmhassany(AT)srttu(DOT)com), Aug 20 2006
f(0) = 1, f(n) = [ n!/e + 1/2 ] for n > 0.
f(n) = n!*Sum((-1)^k/k!, k=0..n).
f(n) = (n-1)*(f(n-1)+a(n-2)), n>0.
f(n) = n*f(n-1)+(-1)^n.
关于f(n)的几种等价形式,倒数第三种即是你需要的那种。