666381 has 4 divisors (see below), whose sum is σ = 888512. Its totient is φ = 444252.

The previous prime is 666353. The next prime is 666403. The reversal of 666381 is 183666.

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.

It is not a de Polignac number, because 666381 - 2¹⁵ = 633613 is a prime.

It is a super-2 number, since 2×666381² = 888127274322, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

It is a Curzon number.

666381 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666301) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 111061 + ... + 111066.

It is an arithmetic number, because the mean of its divisors is an integer number (222128).

2⁶⁶⁶³⁸¹ is an apocalyptic number.

It is an amenable number.

666381 is a deficient number, since it is larger than the sum of its proper divisors (222131).

666381 is a wasteful number, since it uses less digits than its factorization.

666381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 222130.

The product of its digits is 5184, while the sum is 30.

The square root of 666381 is about 816.3216277914. The cubic root of 666381 is about 87.3455670500.

The spelling of 666381 in words is "six hundred sixty-six thousand, three hundred eighty-one".