We investigate thep roperty of an on-symmetricn umericals emigroup generated by three elements. We consider the numerical semigroups generated by at least 4 elements with the property which is said to be neat. The concept of a neat semigroup is a generalization of that of a non-symmetric semigroup generated by three elements. Moreover, the notions of "quasi-toric type" and "toric type" are introduced to neat semigroups. We show that every neat semigroup generated by 4 elements is of quasi-toric type. We give several semigroups of toric type.
Jiryo Komeda (Thu,) studied this question.