21557238 has 16 divisors (see below), whose sum is σ = 43542576. Its totient is φ = 7114400.

The previous prime is 21557231. The next prime is 21557251. The reversal of 21557238 is 83275512.

It is a junction number, because it is equal to n+sod(n) for n = 21557199 and 21557208.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21557231) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 17181 + ... + 18392.

It is an arithmetic number, because the mean of its divisors is an integer number (2721411).

Almost surely, 2^21557238 is an apocalyptic number.

21557238 is an abundant number, since it is smaller than the sum of its proper divisors (21985338).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21557238 is a wasteful number, since it uses less digits than its factorization.

21557238 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35679.

The product of its digits is 16800, while the sum is 33.

The square root of 21557238 is about 4642.9772775666. The cubic root of 21557238 is about 278.3114274735.

The spelling of 21557238 in words is "twenty-one million, five hundred fifty-seven thousand, two hundred thirty-eight".