21388008 has 64 divisors (see below), whose sum is σ = 55618560. Its totient is φ = 6849216.

The previous prime is 21387973. The next prime is 21388009. The reversal of 21388008 is 80088312.

It is not an unprimeable number, because it can be changed into a prime (21388009) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 75435 + ... + 75717.

It is an arithmetic number, because the mean of its divisors is an integer number (869040).

Almost surely, 2^21388008 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 21388008, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27809280).

21388008 is an abundant number, since it is smaller than the sum of its proper divisors (34230552).

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

21388008 is a wasteful number, since it uses less digits than its factorization.

21388008 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 406 (or 402 counting only the distinct ones).

The product of its (nonzero) digits is 3072, while the sum is 30.

The square root of 21388008 is about 4624.7170724272. The cubic root of 21388008 is about 277.5812407214.

The spelling of 21388008 in words is "twenty-one million, three hundred eighty-eight thousand, eight".