21387288 has 48 divisors (see below), whose sum is σ = 57908520. Its totient is φ = 6579456.

The previous prime is 21387287. The next prime is 21387299. The reversal of 21387288 is 88278312.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21387287) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1420 + ... + 6692.

Almost surely, 2^21387288 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 21387288, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28954260).

21387288 is an abundant number, since it is smaller than the sum of its proper divisors (36521232).

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

21387288 is a wasteful number, since it uses less digits than its factorization.

21387288 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5308 (or 5291 counting only the distinct ones).

The product of its digits is 43008, while the sum is 39.

The square root of 21387288 is about 4624.6392291724. The cubic root of 21387288 is about 277.5781258804.

The spelling of 21387288 in words is "twenty-one million, three hundred eighty-seven thousand, two hundred eighty-eight".