OFFSET
1,2
REFERENCES
Valery A. Liskovets, The number of initially connected automata, Kibernetika, (Kiev), No3 (1969), 16-19; Engl. transl.: Cybernetics, v.4 (1969), 259-262.
LINKS
Valery A. Liskovets, Exact enumeration of acyclic automata, Proc. 15th Conf. "Formal Power Series and Algebr. Combin. (FPSAC'03)", 2003.
Valery A. Liskovets, Exact enumeration of acyclic deterministic automata, Discrete Appl. Math., 154, No.3 (2006), 537-551.
FORMULA
a(n) := A006690(n)/n^3
MATHEMATICA
b[1] = 1; b[n_] := b[n] = n^(3n)/(n-1)! - Sum[n^(3(n-i)) b[i]/(n-i)!, {i, 1, n-1}];
a[n_] := b[n]/n^3;
Array[a, 11] (* Jean-François Alcover, Aug 28 2019 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Valery A. Liskovets, Apr 09 2003
STATUS
approved