21638443 has 4 divisors (see below), whose sum is σ = 21656520. Its totient is φ = 21620368.

The previous prime is 21638431. The next prime is 21638479. The reversal of 21638443 is 34483612.

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 21638443 - 2¹³ = 21630251 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21638143) 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, 7105 + ... + 9682.

It is an arithmetic number, because the mean of its divisors is an integer number (5414130).

Almost surely, 2^21638443 is an apocalyptic number.

21638443 is a deficient number, since it is larger than the sum of its proper divisors (18077).

21638443 is a wasteful number, since it uses less digits than its factorization.

21638443 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18076.

The product of its digits is 13824, while the sum is 31.

The square root of 21638443 is about 4651.7139851887. The cubic root of 21638443 is about 278.6604511700.

The spelling of 21638443 in words is "twenty-one million, six hundred thirty-eight thousand, four hundred forty-three".