21636624 has 40 divisors (see below), whose sum is σ = 56460672. Its totient is φ = 7139200.

The previous prime is 21636619. The next prime is 21636647. The reversal of 21636624 is 42663612.

It is a Smith number, since the sum of its digits (30) coincides with the sum of the digits of its 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 = 21636591 and 21636600.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2617 + ... + 7079.

Almost surely, 2^21636624 is an apocalyptic number.

21636624 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21636624, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28230336).

21636624 is an abundant number, since it is smaller than the sum of its proper divisors (34824048).

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

21636624 is a wasteful number, since it uses less digits than its factorization.

21636624 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4575 (or 4569 counting only the distinct ones).

The product of its digits is 10368, while the sum is 30.

The square root of 21636624 is about 4651.5184617499. The cubic root of 21636624 is about 278.6526425742.

The spelling of 21636624 in words is "twenty-one million, six hundred thirty-six thousand, six hundred twenty-four".