400000021 has 4 divisors (see below), whose sum is σ = 423529452. Its totient is φ = 376470592.

The previous prime is 400000009. The next prime is 400000043. The reversal of 400000021 is 120000004.

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 351975121 + 48024900 = 18761^2 + 6930^2 .

It is a cyclic number.

It is not a de Polignac number, because 400000021 - 2⁷ = 399999893 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (400000091) 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, 11764690 + ... + 11764723.

It is an arithmetic number, because the mean of its divisors is an integer number (105882363).

Almost surely, 2^400000021 is an apocalyptic number.

It is an amenable number.

400000021 is a deficient number, since it is larger than the sum of its proper divisors (23529431).

400000021 is a wasteful number, since it uses less digits than its factorization.

400000021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23529430.

The product of its (nonzero) digits is 8, while the sum is 7.

The square root of 400000021 is about 20000.0005250000. Note that the first 3 decimals coincide. The cubic root of 400000021 is about 736.8063126222.

Adding to 400000021 its reverse (120000004), we get a palindrome (520000025).

The spelling of 400000021 in words is "four hundred million, twenty-one", and thus it is an aban number.