21683639 has 4 divisors (see below), whose sum is σ = 21770280. Its totient is φ = 21597000.

The previous prime is 21683611. The next prime is 21683659. The reversal of 21683639 is 93638612.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21683639 is a prime.

It is a Duffinian number.

It is a plaindrome in base 8.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21683659) 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, 42944 + ... + 43445.

It is an arithmetic number, because the mean of its divisors is an integer number (5442570).

Almost surely, 2^21683639 is an apocalyptic number.

21683639 is a deficient number, since it is larger than the sum of its proper divisors (86641).

21683639 is an equidigital number, since it uses as much as digits as its factorization.

21683639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 86640.

The product of its digits is 46656, while the sum is 38.

The square root of 21683639 is about 4656.5694454179. The cubic root of 21683639 is about 278.8543280177.

It can be divided in two parts, 21683 and 639, that added together give a palindrome (22322).

The spelling of 21683639 in words is "twenty-one million, six hundred eighty-three thousand, six hundred thirty-nine".