21522221 has 16 divisors (see below), whose sum is σ = 26582400. Its totient is φ = 17357760.

The previous prime is 21522217. The next prime is 21522223. The reversal of 21522221 is 12222512.

It is not a de Polignac number, because 21522221 - 2² = 21522217 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (17).

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 21522221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21522223) 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, 3986 + ... + 7676.

It is an arithmetic number, because the mean of its divisors is an integer number (1661400).

Almost surely, 2^21522221 is an apocalyptic number.

It is an amenable number.

21522221 is a deficient number, since it is larger than the sum of its proper divisors (5060179).

21522221 is an equidigital number, since it uses as much as digits as its factorization.

21522221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3729 (or 3715 counting only the distinct ones).

The product of its digits is 160, while the sum is 17.

The square root of 21522221 is about 4639.2047809943. The cubic root of 21522221 is about 278.1606519293.

Adding to 21522221 its reverse (12222512), we get a palindrome (33744733).

The spelling of 21522221 in words is "twenty-one million, five hundred twenty-two thousand, two hundred twenty-one".