onedigit

Onedigit is a term used in numeration to denote an integer that can be represented with a single symbol in a given numeral system. In common usage, it most often refers to the one-digit numbers in base-10, the digits 0 through 9.

In base-10, the set {0,1,2,3,4,5,6,7,8,9} comprises all one-digit numbers. They are the building blocks of larger numbers, forming the units place in decimal notation; numbers with more than one digit are constructed by combining these digits with place value.

In other bases, the concept remains the same: a one-digit number ranges from 0 to base-1. For example, base-2 uses 0 and 1; base-16 uses 0–9 and A–F. Decimal digits are typically represented with the symbols 0–9 in most contexts.

Some properties are commonly noted. 0 is the additive identity, 1 is the multiplicative identity, and among one-digit numbers 1 is not prime and 0 is not prime or composite; the one-digit primes are 2, 3, 5, and 7; the one-digit composites are 4, 6, 8, and 9.

Applications include early arithmetic learning and digital systems. In computing, four-bit binary coded decimal encodes decimal digits 0–9 as 0000 to 1001, and one-digit values appear in displays, counters, and compact encodings of decimal data. See also single-digit numbers and base (numeration) for related concepts.