21228557 has 4 divisors (see below), whose sum is σ = 24261216. Its totient is φ = 18195900.

The previous prime is 21228553. The next prime is 21228569. The reversal of 21228557 is 75582212.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21228557 - 2² = 21228553 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21228553) 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, 1516319 + ... + 1516332.

It is an arithmetic number, because the mean of its divisors is an integer number (6065304).

Almost surely, 2^21228557 is an apocalyptic number.

It is an amenable number.

21228557 is a deficient number, since it is larger than the sum of its proper divisors (3032659).

21228557 is an equidigital number, since it uses as much as digits as its factorization.

21228557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3032658.

The product of its digits is 11200, while the sum is 32.

The square root of 21228557 is about 4607.4458217108. The cubic root of 21228557 is about 276.8897152929.

The spelling of 21228557 in words is "twenty-one million, two hundred twenty-eight thousand, five hundred fifty-seven".