987654321

987654321 is the nine-digit integer consisting of the digits 9 through 1 in descending order. It is a notable example of a descending pandigital number in base-10, since it uses each of the digits from 1 to 9 exactly once.

Numerically, the digits sum to 45, which makes the number divisible by 9 and by 3. The exact factorization is 987654321 = 9 × 109,739,369, or 3^2 × 109,739,369, indicating that the value is composite rather than prime.

As a decimal, the number is 987,654,321 and is approximately 9.88 × 10^8. Its digital root is 9, reflecting the divisibility by 9. Its status as a pandigital arrangement of the digits 1–9 gives it distinctive combinatorial properties, though it does not hold a particular universal arithmetic significance beyond common digit-sum and permutation considerations.

In educational and puzzle contexts, 987654321 is often cited to illustrate digit permutations and pandigital concepts, rather than for a unique mathematical theorem. It is sometimes used as a sample number in discussions of digit symmetry, numeral systems, and recreational math, where it serves as a concrete, memorable example of a full set of digits arranged in descending order.