21538720 has 48 divisors (see below), whose sum is σ = 58157568. Its totient is φ = 7384320.

The previous prime is 21538703. The next prime is 21538721. The reversal of 21538720 is 2783512.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is not an unprimeable number, because it can be changed into a prime (21538721) 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, 8496 + ... + 10735.

It is an arithmetic number, because the mean of its divisors is an integer number (1211616).

Almost surely, 2^21538720 is an apocalyptic number.

21538720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21538720 is an abundant number, since it is smaller than the sum of its proper divisors (36618848).

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

21538720 is a wasteful number, since it uses less digits than its factorization.

21538720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19253 (or 19245 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 28.

The square root of 21538720 is about 4640.9826545679. The cubic root of 21538720 is about 278.2317133740.

The spelling of 21538720 in words is "twenty-one million, five hundred thirty-eight thousand, seven hundred twenty".