21636636 has 72 divisors (see below), whose sum is σ = 60673536. Its totient is φ = 5977440.

The previous prime is 21636619. The next prime is 21636647. The reversal of 21636636 is 63663612.

It is a happy number.

It is a hoax number, since the sum of its digits (33) coincides with the sum of the digits of its distinct prime factors.

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 21636597 and 21636606.

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, 17635 + ... + 18821.

It is an arithmetic number, because the mean of its divisors is an integer number (842688).

Almost surely, 2^21636636 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 21636636, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30336768).

21636636 is an abundant number, since it is smaller than the sum of its proper divisors (39036900).

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

21636636 is a wasteful number, since it uses less digits than its factorization.

21636636 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1239 (or 1230 counting only the distinct ones).

The product of its digits is 23328, while the sum is 33.

The square root of 21636636 is about 4651.5197516511. The cubic root of 21636636 is about 278.6526940892.

The spelling of 21636636 in words is "twenty-one million, six hundred thirty-six thousand, six hundred thirty-six".