21013668 has 72 divisors (see below), whose sum is σ = 59358208. Its totient is φ = 6461856.

The previous prime is 21013633. The next prime is 21013709. The reversal of 21013668 is 86631012.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 11805 + ... + 13467.

Almost surely, 2^21013668 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 21013668, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29679104).

21013668 is an abundant number, since it is smaller than the sum of its proper divisors (38344540).

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

21013668 is a wasteful number, since it uses less digits than its factorization.

21013668 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1695 (or 1681 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 21013668 is about 4584.0667534407. The cubic root of 21013668 is about 275.9522601739.

The spelling of 21013668 in words is "twenty-one million, thirteen thousand, six hundred sixty-eight".