Number of r-bicoverings (or restricted proper 2-covers) of an n-set.

A060053

Number of r-bicoverings (or restricted proper 2-covers) of an n-set.

Terms

    a(0) =1a(1) =0a(2) =1a(3) =5a(4) =43a(5) =518a(6) =8186a(7) =163356a(8) =3988342a(9) =116396952a(10) =3985947805a(11) =157783127673

External references