21637812 has 60 divisors (see below), whose sum is σ = 58977856. Its totient is φ = 6174000.

The previous prime is 21637807. The next prime is 21637849. The reversal of 21637812 is 21873612.

It is a self number, because there is not a number n which added to its sum of digits gives 21637812.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 28437 + ... + 29187.

Almost surely, 2^21637812 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 21637812, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29488928).

21637812 is an abundant number, since it is smaller than the sum of its proper divisors (37340044).

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

21637812 is an equidigital number, since it uses as much as digits as its factorization.

21637812 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 786 (or 763 counting only the distinct ones).

The product of its digits is 4032, while the sum is 30.

The square root of 21637812 is about 4651.6461602319. The cubic root of 21637812 is about 278.6577424653.

The spelling of 21637812 in words is "twenty-one million, six hundred thirty-seven thousand, eight hundred twelve".