399640081 has 3 divisors (see below), whose sum is σ = 399660073. Its totient is φ = 399620090.

The previous prime is 399640061. The next prime is 399640093. The reversal of 399640081 is 180046993.

The square root of 399640081 is 19991.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is not a de Polignac number, because 399640081 - 2⁷ = 399639953 is a prime.

It is a super-2 number, since 2×399640081² = 319424388683373122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (399640001) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 9996 + ... + 29986.

Almost surely, 2^399640081 is an apocalyptic number.

399640081 is the 19991-st square number.

399640081 is the 9996-th centered octagonal number.

It is an amenable number.

399640081 is a deficient number, since it is larger than the sum of its proper divisors (19992).

399640081 is an frugal number, since it uses more digits than its factorization.

399640081 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39982 (or 19991 counting only the distinct ones).

The product of its (nonzero) digits is 46656, while the sum is 40.

The cubic root of 399640081 is about 736.5852412567.

Multiplying 399640081 by its product of nonzero digits (46656), we get a square (18645607619136 = 4318056²).

The spelling of 399640081 in words is "three hundred ninety-nine million, six hundred forty thousand, eighty-one".