400821 has 16 divisors (see below), whose sum is σ = 576384. Its totient is φ = 247104.

The previous prime is 400759. The next prime is 400823. The reversal of 400821 is 128004.

400821 is digitally balanced in base 7, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 400821 - 2¹³ = 392629 is a prime.

400821 is strictly pandigital in base 7.

It is a self number, because there is not a number n which added to its sum of digits gives 400821.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (400823) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2475 + ... + 2631.

It is an arithmetic number, because the mean of its divisors is an integer number (36024).

2⁴⁰⁰⁸²¹ is an apocalyptic number.

It is an amenable number.

400821 is a deficient number, since it is larger than the sum of its proper divisors (175563).

400821 is a wasteful number, since it uses less digits than its factorization.

400821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 220.

The product of its (nonzero) digits is 64, while the sum is 15.

The square root of 400821 is about 633.1042568172. The cubic root of 400821 is about 73.7310053544.

Adding to 400821 its reverse (128004), we get a palindrome (528825).

It can be divided in two parts, 400 and 821, that added together give a palindrome (1221).

The spelling of 400821 in words is "four hundred thousand, eight hundred twenty-one".