21640211 has 4 divisors (see below), whose sum is σ = 21650424. Its totient is φ = 21630000.

The previous prime is 21640189. The next prime is 21640219. The reversal of 21640211 is 11204612.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21640211 - 2⁶ = 21640147 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 21640211.

It is not an unprimeable number, because it can be changed into a prime (21640219) 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, 605 + ... + 6606.

It is an arithmetic number, because the mean of its divisors is an integer number (5412606).

Almost surely, 2^21640211 is an apocalyptic number.

21640211 is a deficient number, since it is larger than the sum of its proper divisors (10213).

21640211 is an equidigital number, since it uses as much as digits as its factorization.

21640211 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10212.

The product of its (nonzero) digits is 96, while the sum is 17.

The square root of 21640211 is about 4651.9040187863. The cubic root of 21640211 is about 278.6680404138.

Adding to 21640211 its reverse (11204612), we get a palindrome (32844823).

It can be divided in two parts, 21 and 640211, that multiplied together give a palindrome (13444431).

The spelling of 21640211 in words is "twenty-one million, six hundred forty thousand, two hundred eleven".