Double-Struck Capital Z ℤ

The set of integers ℤ = {…, -2, -1, 0, 1, 2, ...} consists of the natural numbers (positive integers), their negative counterparts, and zero. The term «integer» comes from the German word «Zahl,» meaning «number.» The set ℤ is countable (equivalent in cardinality to the set of natural numbers ℕ).

The sets ℕ , ℤ , ℚ , ℝ , ℂ are often written in bold font (for example, in the works of Nicolas Bourbaki) or as double-struck letters on blackboards and manuscripts. American mathematicians introduced the usage of double-struck font in printed texts, and it became popularized with the famous textbook on complex analysis by Gunning and Rossi, published in 1965.

Il simbolo «Double-Struck Capital Z» è incluso nel sotto-blocco «Simboli simili a lettere» del blocco «lettere simboli» ed è stato approvato come parte della versione Unicode 1.1 nel 1993.