21388528 has 90 divisors (see below), whose sum is σ = 52251864. Its totient is φ = 8306496.

The previous prime is 21388517. The next prime is 21388529. The reversal of 21388528 is 82588312.

21388528 = 802² + 803² + ... + 833².

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21388529) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 929925 + ... + 929947.

Almost surely, 2^21388528 is an apocalyptic number.

21388528 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21388528, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26125932).

21388528 is an abundant number, since it is smaller than the sum of its proper divisors (30863336).

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

21388528 is a wasteful number, since it uses less digits than its factorization.

21388528 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99 (or 51 counting only the distinct ones).

The product of its digits is 30720, while the sum is 37.

The square root of 21388528 is about 4624.7732917409. The cubic root of 21388528 is about 277.5834902854.

The spelling of 21388528 in words is "twenty-one million, three hundred eighty-eight thousand, five hundred twenty-eight".