21228215 has 4 divisors (see below), whose sum is σ = 25473864. Its totient is φ = 16982568.

The previous prime is 21228209. The next prime is 21228217. The reversal of 21228215 is 51282212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21228215 - 2¹⁴ = 21211831 is a prime.

It is a super-2 number, since 2×21228215² = 901274224172450, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21228217) 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, 2122817 + ... + 2122826.

It is an arithmetic number, because the mean of its divisors is an integer number (6368466).

Almost surely, 2^21228215 is an apocalyptic number.

21228215 is a deficient number, since it is larger than the sum of its proper divisors (4245649).

21228215 is an equidigital number, since it uses as much as digits as its factorization.

21228215 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4245648.

The product of its digits is 640, while the sum is 23.

The square root of 21228215 is about 4607.4087077228. The cubic root of 21228215 is about 276.8882283526. Note that the first 3 decimals are identical.

The spelling of 21228215 in words is "twenty-one million, two hundred twenty-eight thousand, two hundred fifteen".