381

381 is a natural number that follows 380 and precedes 382. It is an odd composite number with prime factors 3 and 127 (381 = 3 × 127). In base 16 it is written as 0x17D and in base 2 it is 101111101. In Roman numerals it is CCCLXXXI.

Historically, the year AD 381 is notable for the First Council of Constantinople, convened under Emperor Theodosius I. The council reaffirmed the Nicene Creed and clarified the doctrine of the Holy Spirit, addressing theological disputes and shaping orthodox Christian doctrine for centuries.

In modern usage, 381 is the international calling code for Serbia. The code is used to reach Serbian telephone numbers from abroad and is followed by city or local area codes and subscriber numbers.