[1] L. BABAI: On the abstract group of automorphisms "Combinatorics". Proc. 8th British Comb. Conf. Swansea 1981, London Math. Soc. Lecture Note 52, 1-40. MR 0633647

[2] A. H. CLIFFORD G. B. PRESTON: The algebraic theory of semigroups. Amer. Math. Soc. Providence, Rhode Island 1967. MR 0218472

[3] P. X. GALLAGHER: Counting finite groups of given order. Math. Z. 102 (1967), 236-237. MR 0222158 | Zbl 0189.02304

[4] Z. HEDRLÍN A. PULTR: Symmetric relations (undirected graphs) with given semigroups. Monatsh. Math. 69 (1965), 318-322. MR 0188082

[5] D. J. KLEITMAN B. P. ROTHSCHILD J. H. SPENCER: The number of semigroups of order $n$. Proc. Amer. Math. Soc. 55 (1976), 227-232. MR 0414380

[6] V. KOUBEK V. RÖDL: On the minimum order of graphs with given semigroup. J. of Comb.Theory B, 36 (1984), 135-155. MR 0746545