21013812 has 72 divisors (see below), whose sum is σ = 56871360. Its totient is φ = 6526080.

The previous prime is 21013787. The next prime is 21013823. The reversal of 21013812 is 21831012.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

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, 33639 + ... + 34257.

It is an arithmetic number, because the mean of its divisors is an integer number (789880).

Almost surely, 2^21013812 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 21013812, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28435680).

21013812 is an abundant number, since it is smaller than the sum of its proper divisors (35857548).

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

21013812 is a wasteful number, since it uses less digits than its factorization.

21013812 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 693 (or 688 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 18.

The square root of 21013812 is about 4584.0824599913. The cubic root of 21013812 is about 275.9528905102.

Adding to 21013812 its reverse (21831012), we get a palindrome (42844824).

The spelling of 21013812 in words is "twenty-one million, thirteen thousand, eight hundred twelve".