21156636 has 48 divisors (see below), whose sum is σ = 52720416. Its totient is φ = 6580224.

The previous prime is 21156613. The next prime is 21156647. The reversal of 21156636 is 63665112.

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 15 ways as a sum of consecutive naturals, for example, 27570 + ... + 28326.

It is an arithmetic number, because the mean of its divisors is an integer number (1098342).

Almost surely, 2^21156636 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 21156636, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26360208).

21156636 is an abundant number, since it is smaller than the sum of its proper divisors (31563780).

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

21156636 is a wasteful number, since it uses less digits than its factorization.

21156636 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 918 (or 916 counting only the distinct ones).

The product of its digits is 6480, while the sum is 30.

The square root of 21156636 is about 4599.6343332922. The cubic root of 21156636 is about 276.5766665858.

The spelling of 21156636 in words is "twenty-one million, one hundred fifty-six thousand, six hundred thirty-six".