381781 has 4 divisors (see below), whose sum is σ = 389952. Its totient is φ = 373612.

The previous prime is 381761. The next prime is 381791. The reversal of 381781 is 187183.

381781 = T₅₀₃ + T₅₀₄ + T₅₀₅.

It is a happy number.

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: 187183 = 37 ⋅5059.

It is a cyclic number.

It is not a de Polignac number, because 381781 - 2⁵ = 381749 is a prime.

It is a super-2 number, since 2×381781² = 291513463922, which contains 22 as substring.

It is a Duffinian number.

381781 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (381761) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4015 + ... + 4108.

It is an arithmetic number, because the mean of its divisors is an integer number (97488).

2³⁸¹⁷⁸¹ is an apocalyptic number.

381781 is the 505-th centered triangular number.

It is an amenable number.

381781 is a deficient number, since it is larger than the sum of its proper divisors (8171).

381781 is an equidigital number, since it uses as much as digits as its factorization.

381781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8170.

The product of its digits is 1344, while the sum is 28.

The square root of 381781 is about 617.8842933754. The cubic root of 381781 is about 72.5445465434.

The spelling of 381781 in words is "three hundred eighty-one thousand, seven hundred eighty-one".