378

378 is a natural number that follows 377 and precedes 379. It is even and composite, with prime factorization 2 × 3^3 × 7. The sum of its digits is 18, and since 378 is divisible by 18 it is a Harshad (Niven) number in base 10. It is also a multiple of 9 (378 ÷ 9 = 42) and of 3.

As a triangular number, 378 equals 27 × 28 / 2, so it is the 27th triangular number.

In Roman numerals, 378 is written as CCCLXXVIII.

In the calendar, the year 378 CE is known for the Battle of Adrianople on August 9, where Gothic forces under Fritigern defeated the Roman army, and Emperor Valens was killed. The battle is considered a turning point in the decline of the Western Roman Empire, contributing to broader pressures on the late Roman state.

Because it is divisible by 9 and by 18, 378 also serves as an example in number theory discussions of divisibility rules and digit-sum properties in base 10. Its factorization and triangular status make it a common reference in introductory arithmetic and early number theory.