20640221 has 12 divisors (see below), whose sum is σ = 24372288. Its totient is φ = 17424792.

The previous prime is 20640181. The next prime is 20640233. The reversal of 20640221 is 12204602.

It is not a de Polignac number, because 20640221 - 2⁶ = 20640157 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20640221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20640121) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 140 + ... + 6426.

It is an arithmetic number, because the mean of its divisors is an integer number (2031024).

Almost surely, 2^20640221 is an apocalyptic number.

It is an amenable number.

20640221 is a deficient number, since it is larger than the sum of its proper divisors (3732067).

20640221 is an equidigital number, since it uses as much as digits as its factorization.

20640221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6368 (or 6361 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 17.

The square root of 20640221 is about 4543.1509990314. The cubic root of 20640221 is about 274.3077730456.

Adding to 20640221 its reverse (12204602), we get a palindrome (32844823).

The spelling of 20640221 in words is "twenty million, six hundred forty thousand, two hundred twenty-one".