400021 has 4 divisors (see below), whose sum is σ = 401632. Its totient is φ = 398412.

The previous prime is 400009. The next prime is 400031. The reversal of 400021 is 120004.

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.

It is a cyclic number.

It is not a de Polignac number, because 400021 - 2⁵ = 399989 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 399977 and 400013.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (400031) 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, 345 + ... + 958.

It is an arithmetic number, because the mean of its divisors is an integer number (100408).

2⁴⁰⁰⁰²¹ is an apocalyptic number.

It is an amenable number.

400021 is a deficient number, since it is larger than the sum of its proper divisors (1611).

400021 is a wasteful number, since it uses less digits than its factorization.

400021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1610.

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

The square root of 400021 is about 632.4721337735. The cubic root of 400021 is about 73.6819193613.

Adding to 400021 its reverse (120004), we get a palindrome (520025).

The spelling of 400021 in words is "four hundred thousand, twenty-one", and thus it is an iban number.