21720211 has 12 divisors (see below), whose sum is σ = 23911720. Its totient is φ = 19673280.

The previous prime is 21720197. The next prime is 21720229. The reversal of 21720211 is 11202712.

It is not a de Polignac number, because 21720211 - 2⁹ = 21719699 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21720241) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 8971 + ... + 11131.

Almost surely, 2^21720211 is an apocalyptic number.

21720211 is a deficient number, since it is larger than the sum of its proper divisors (2191509).

21720211 is a wasteful number, since it uses less digits than its factorization.

21720211 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2226 (or 2203 counting only the distinct ones).

The product of its (nonzero) digits is 56, while the sum is 16.

The square root of 21720211 is about 4660.4947162292. The cubic root of 21720211 is about 279.0110134697.

Adding to 21720211 its reverse (11202712), we get a palindrome (32922923).

The spelling of 21720211 in words is "twenty-one million, seven hundred twenty thousand, two hundred eleven".