21639860 has 96 divisors (see below), whose sum is σ = 54190080. Its totient is φ = 7171200.

The previous prime is 21639833. The next prime is 21639869. The reversal of 21639860 is 6893612.

It is a self number, because there is not a number n which added to its sum of digits gives 21639860.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21639869) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 129497 + ... + 129663.

It is an arithmetic number, because the mean of its divisors is an integer number (564480).

Almost surely, 2^21639860 is an apocalyptic number.

21639860 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21639860, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27095040).

21639860 is an abundant number, since it is smaller than the sum of its proper divisors (32550220).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21639860 is a wasteful number, since it uses less digits than its factorization.

21639860 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 237 (or 235 counting only the distinct ones).

The product of its (nonzero) digits is 15552, while the sum is 35.

The square root of 21639860 is about 4651.8662921456. The cubic root of 21639860 is about 278.6665337586. Note that the first 3 decimals are identical.

The spelling of 21639860 in words is "twenty-one million, six hundred thirty-nine thousand, eight hundred sixty".