a(n) = floor(n^n / (n+1)).

Terms

a(0) =1a(1) =0a(2) =1a(3) =6a(4) =51a(5) =520a(6) =6665a(7) =102942a(8) =1864135a(9) =38742048a(10) =909090909a(11) =23775972550a(12) =685853880635