123456789

123456789 is a nine-digit decimal integer formed by the digits 1 through 9 in ascending order. In common usage it is also written with a thousands separator as 123,456,789.

Mathematically, the number has several notable properties. The sum of its digits is 45, so the number is divisible by 9 and by 3. Its prime factorization is 3^2 × 3607 × 3803. Notable arithmetic relationships include 123456789 × 8 = 987654312 and 123456789 × 9 = 1,111,111,101, which exhibit a reflective symmetry in the products.

Uniqueness and representation are also features of this number. It is the only nine-digit number whose digits form a strictly increasing sequence from 1 to 9, making it a canonical example of concatenating consecutive digits in ascending order. This property contributes to its use as a simple reference form in teaching and demonstrations.

Usage and occurrences span education, puzzles, and computational testing. It is commonly employed as an example in digit-sum, place-value, and modular arithmetic explanations, as well as a test value for string handling, pattern recognition, and basic benchmarking in programming exercises.

In decimal notation, 123456789 is specific to base-10 representation. In other numeral bases the same digit sequence would not occur identically, since the available symbols and positional values differ.