393640021 has 4 divisors (see below), whose sum is σ = 393789100. Its totient is φ = 393490944.

The previous prime is 393639989. The next prime is 393640031. The reversal of 393640021 is 120046393.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 97318225 + 296321796 = 9865^2 + 17214^2 .

It is a cyclic number.

It is not a de Polignac number, because 393640021 - 2⁵ = 393639989 is a prime.

It is a super-2 number, since 2×393640021² = 309904932265760882, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (393640031) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 70506 + ... + 75883.

It is an arithmetic number, because the mean of its divisors is an integer number (98447275).

Almost surely, 2^393640021 is an apocalyptic number.

It is an amenable number.

393640021 is a deficient number, since it is larger than the sum of its proper divisors (149079).

393640021 is a wasteful number, since it uses less digits than its factorization.

393640021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 149078.

The product of its (nonzero) digits is 3888, while the sum is 28.

The square root of 393640021 is about 19840.3634291310. The cubic root of 393640021 is about 732.8803576999.

The spelling of 393640021 in words is "three hundred ninety-three million, six hundred forty thousand, twenty-one".