381991 has 2 divisors, whose sum is σ = 381992. Its totient is φ = 381990.

The previous prime is 381989. The next prime is 382001. The reversal of 381991 is 199183.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 381991 - 2¹ = 381989 is a prime.

Together with 381989, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (381911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 190995 + 190996.

It is an arithmetic number, because the mean of its divisors is an integer number (190996).

2³⁸¹⁹⁹¹ is an apocalyptic number.

381991 is a deficient number, since it is larger than the sum of its proper divisors (1).

381991 is an equidigital number, since it uses as much as digits as its factorization.

381991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1944, while the sum is 31.

The square root of 381991 is about 618.0542047426. The cubic root of 381991 is about 72.5578452341.

The spelling of 381991 in words is "three hundred eighty-one thousand, nine hundred ninety-one".