399981 has 4 divisors (see below), whose sum is σ = 533312. Its totient is φ = 266652.

The previous prime is 399979. The next prime is 399983. The reversal of 399981 is 189993.

399981 is digitally balanced in base 7, because in such base it contains all the possibile digits an equal number of times.

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: 189993 = 3 ⋅63331.

It is an interprime number because it is at equal distance from previous prime (399979) and next prime (399983).

It is not a de Polignac number, because 399981 - 2¹ = 399979 is a prime.

It is a super-2 number, since 2×399981² = 319969600722, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

399981 is strictly pandigital in base 7.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (399983) 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, 66661 + ... + 66666.

It is an arithmetic number, because the mean of its divisors is an integer number (133328).

2³⁹⁹⁹⁸¹ is an apocalyptic number.

It is an amenable number.

399981 is a deficient number, since it is larger than the sum of its proper divisors (133331).

399981 is a wasteful number, since it uses less digits than its factorization.

399981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 133330.

The product of its digits is 17496, while the sum is 39.

The square root of 399981 is about 632.4405110364. The cubic root of 399981 is about 73.6794633444.

The spelling of 399981 in words is "three hundred ninety-nine thousand, nine hundred eighty-one".