21539388 has 96 divisors (see below), whose sum is σ = 58643200. Its totient is φ = 6132672.

The previous prime is 21539387. The next prime is 21539411. The reversal of 21539388 is 88393512.

It is a Harshad number since it is a multiple of its sum of digits (39).

Its product of digits (51840) is a multiple of the sum of its prime divisors (80).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21539387) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 500895 + ... + 500937.

Almost surely, 2^21539388 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 21539388, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29321600).

21539388 is an abundant number, since it is smaller than the sum of its proper divisors (37103812).

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

21539388 is a wasteful number, since it uses less digits than its factorization.

21539388 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 108 (or 80 counting only the distinct ones).

The product of its digits is 51840, while the sum is 39.

The square root of 21539388 is about 4641.0546215273. The cubic root of 21539388 is about 278.2345896957.

The spelling of 21539388 in words is "twenty-one million, five hundred thirty-nine thousand, three hundred eighty-eight".