21537216 has 84 divisors (see below), whose sum is σ = 62407800. Its totient is φ = 7100928.

The previous prime is 21537179. The next prime is 21537251. The reversal of 21537216 is 61273512.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 21537216.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 79930 + ... + 80198.

It is an arithmetic number, because the mean of its divisors is an integer number (742950).

Almost surely, 2^21537216 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21537216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31203900).

21537216 is an abundant number, since it is smaller than the sum of its proper divisors (40870584).

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

21537216 is a wasteful number, since it uses less digits than its factorization.

21537216 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 426 (or 413 counting only the distinct ones).

The product of its digits is 2520, while the sum is 27.

The square root of 21537216 is about 4640.8206170892. The cubic root of 21537216 is about 278.2252371266.

The spelling of 21537216 in words is "twenty-one million, five hundred thirty-seven thousand, two hundred sixteen".