636400221 has 16 divisors (see below), whose sum is σ = 865013760. Its totient is φ = 416098800.

The previous prime is 636400213. The next prime is 636400249. The reversal of 636400221 is 122004636.

It is not a de Polignac number, because 636400221 - 2³ = 636400213 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 636400191 and 636400200.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (636400211) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 26896 + ... + 44678.

It is an arithmetic number, because the mean of its divisors is an integer number (54063360).

Almost surely, 2^636400221 is an apocalyptic number.

It is an amenable number.

636400221 is a deficient number, since it is larger than the sum of its proper divisors (228613539).

636400221 is a wasteful number, since it uses less digits than its factorization.

636400221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18016.

The product of its (nonzero) digits is 1728, while the sum is 24.

The square root of 636400221 is about 25226.9740753821. The cubic root of 636400221 is about 860.1551103855.

Adding to 636400221 its reverse (122004636), we get a palindrome (758404857).

The spelling of 636400221 in words is "six hundred thirty-six million, four hundred thousand, two hundred twenty-one".