21638635 has 4 divisors (see below), whose sum is σ = 25966368. Its totient is φ = 17310904.

The previous prime is 21638633. The next prime is 21638647. The reversal of 21638635 is 53683612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21638635 - 2¹ = 21638633 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21638635.

It is not an unprimeable number, because it can be changed into a prime (21638633) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2163859 + ... + 2163868.

It is an arithmetic number, because the mean of its divisors is an integer number (6491592).

Almost surely, 2^21638635 is an apocalyptic number.

21638635 is a deficient number, since it is larger than the sum of its proper divisors (4327733).

21638635 is an equidigital number, since it uses as much as digits as its factorization.

21638635 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4327732.

The product of its digits is 25920, while the sum is 34.

The square root of 21638635 is about 4651.7346226972. The cubic root of 21638635 is about 278.6612753613.

The spelling of 21638635 in words is "twenty-one million, six hundred thirty-eight thousand, six hundred thirty-five".