Number of maps f: [n] -> [n] with f(x)<=x and f(f(x)) = f(f(f(x))).
A187761
Number of maps f: [n] -> [n] with f(x)<=x and f(f(x)) = f(f(f(x))).
Terms
- a(0) =1a(1) =1a(2) =2a(3) =6a(4) =23a(5) =106a(6) =568a(7) =3459a(8) =23544a(9) =176850a(10) =1451253a(11) =12904312a(12) =123489888a(13) =1264591561a(14) =13790277294a(15) =159466823794
External references
- oeis: A187761