21811639 has 4 divisors (see below), whose sum is σ = 22959640. Its totient is φ = 20663640.

The previous prime is 21811637. The next prime is 21811661. The reversal of 21811639 is 93611812.

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

It is not a de Polignac number, because 21811639 - 2¹ = 21811637 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 21811639.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21811637) 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, 573972 + ... + 574009.

It is an arithmetic number, because the mean of its divisors is an integer number (5739910).

Almost surely, 2^21811639 is an apocalyptic number.

21811639 is a deficient number, since it is larger than the sum of its proper divisors (1148001).

21811639 is a wasteful number, since it uses less digits than its factorization.

21811639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1148000.

The product of its digits is 2592, while the sum is 31.

The square root of 21811639 is about 4670.2932456110. The cubic root of 21811639 is about 279.4019505820.

The spelling of 21811639 in words is "twenty-one million, eight hundred eleven thousand, six hundred thirty-nine".