• 381 can be written using four 4's:
381 has 4 divisors (see below), whose sum is σ = 512. Its totient is φ = 252.
The previous prime is 379. The next prime is 383. The reversal of 381 is 183.
381 is nontrivially palindromic in base 2 and base 8.
381 is an esthetic number in base 13, because in such base its adjacent digits differ by 1.
It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 183 = 3 ⋅61.
It is an interprime number because it is at equal distance from previous prime (379) and next prime (383).
It is not a de Polignac number, because 381 - 21 = 379 is a prime.
It is a super-2 number, since 2×3812 = 290322, which contains 22 as substring.
It is a D-number.
It is an alternating number because its digits alternate between odd and even.
It is the 20-th Hogben number.
It is a Duffinian number.
381 is an undulating number in base 8.
It is a plaindrome in base 12, base 13 and base 16.
It is a congruent number.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 381.
It is not an unprimeable number, because it can be changed into a prime (383) by changing a digit.
It is a nontrivial repunit in base 19.
It is a pernicious number, because its binary representation contains a prime number (7) of ones.
It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 61 + ... + 66.
It is an arithmetic number, because the mean of its divisors is an integer number (128).
It is an amenable number.
381 is a deficient number, since it is larger than the sum of its proper divisors (131).
381 is a wasteful number, since it uses less digits than its factorization.
381 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 130.
The product of its digits is 24, while the sum is 12.
The square root of 381 is about 19.5192212959. The cubic root of 381 is about 7.2495045242.
Adding to 381 its sum of digits (12), we get a palindrome (393).
It can be divided in two parts, 3 and 81, that multiplied together give a 5-th power (243 = 35).
The spelling of 381 in words is "three hundred eighty-one", and thus it is an aban number.
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