399665 has 16 divisors (see below), whose sum is σ = 577920. Its totient is φ = 259200.

The previous prime is 399647. The next prime is 399667. The reversal of 399665 is 566993.

399665 = T₂₀ + T₂₁ + ... + T₁₃₃.

It is not a de Polignac number, because 399665 - 2⁶ = 399601 is a prime.

It is a super-2 number, since 2×399665² = 319464224450, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (399667) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 365 + ... + 965.

It is an arithmetic number, because the mean of its divisors is an integer number (36120).

2³⁹⁹⁶⁶⁵ is an apocalyptic number.

399665 is a gapful number since it is divisible by the number (35) formed by its first and last digit.

It is an amenable number.

399665 is a deficient number, since it is larger than the sum of its proper divisors (178255).

399665 is a wasteful number, since it uses less digits than its factorization.

399665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 632.

The product of its digits is 43740, while the sum is 38.

The square root of 399665 is about 632.1906358054. The cubic root of 399665 is about 73.6600550520.

The spelling of 399665 in words is "three hundred ninety-nine thousand, six hundred sixty-five".