This paper illustrates the system of representing natural numbers introduced by G. Lemaître [Acad. Roy. Belgique, Bull. Cl. Sci., V. Sér. 40, 683-691 (1954; Zbl 0055.36307)] with the aim to make written calculations with natural numbers by a pure mechanic manipulation. The paper presents the system in a little modified form. The ciphers 0-1 are, in fact, used instead of the letters \(ijkl\) of the original. The algorithms for the arithmetic operations are presented by numerical examples.