Double-Struck Italic Small I

Double-Struck Italic Small I at U+2148 is a letterlike mathematical symbol used as a styled lowercase i, most notably for the imaginary unit. It is part of the Letterlike Symbols block, where Unicode encodes a small set of symbols that function like letters but have established symbolic meanings or compatibility with mathematical typography. In mathematics, engineering, and physics, ⅈ can stand for the square root of minus one when a text wants the imaginary unit to be visibly distinct from an ordinary variable i. It may appear in formulas for complex numbers, such as a + bⅈ, especially in material that follows a convention of using a double-struck italic form for constants. Its practical use is much narrower than plain italic i or the standard mathematical italic i found in equation layout systems. Most textbooks, papers, and calculators simply use i, while electrical engineering often uses j instead to avoid confusion with current. This character is therefore seen mainly in specialized Unicode math text, symbol charts, font testing, and copied formulas where the exact letterlike symbol matters.