21445221 has 16 divisors (see below), whose sum is σ = 33216128. Its totient is φ = 12052800.

The previous prime is 21445217. The next prime is 21445247. The reversal of 21445221 is 12254412.

It is not a de Polignac number, because 21445221 - 2² = 21445217 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21445201) 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 15 ways as a sum of consecutive naturals, for example, 7090 + ... + 9651.

It is an arithmetic number, because the mean of its divisors is an integer number (2076008).

Almost surely, 2^21445221 is an apocalyptic number.

21445221 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21445221 is a deficient number, since it is larger than the sum of its proper divisors (11770907).

21445221 is a wasteful number, since it uses less digits than its factorization.

21445221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16812.

The product of its digits is 640, while the sum is 21.

The square root of 21445221 is about 4630.8985089289. The cubic root of 21445221 is about 277.8285306316.

21445221 divided by its sum of digits (21) gives a palindrome (1021201).

Adding to 21445221 its reverse (12254412), we get a palindrome (33699633).

The spelling of 21445221 in words is "twenty-one million, four hundred forty-five thousand, two hundred twenty-one".