21553639 has 4 divisors (see below), whose sum is σ = 21635856. Its totient is φ = 21471424.

The previous prime is 21553633. The next prime is 21553643. The reversal of 21553639 is 93635512.

It is a happy number.

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 21553639 - 2¹¹ = 21551591 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21553633) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 40714 + ... + 41239.

It is an arithmetic number, because the mean of its divisors is an integer number (5408964).

Almost surely, 2^21553639 is an apocalyptic number.

21553639 is a deficient number, since it is larger than the sum of its proper divisors (82217).

21553639 is an equidigital number, since it uses as much as digits as its factorization.

21553639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 82216.

The product of its digits is 24300, while the sum is 34.

The square root of 21553639 is about 4642.5896868020. The cubic root of 21553639 is about 278.2959384983.

The spelling of 21553639 in words is "twenty-one million, five hundred fifty-three thousand, six hundred thirty-nine".