21639828 has 48 divisors (see below), whose sum is σ = 58513280. Its totient is φ = 6096384.

The previous prime is 21639823. The next prime is 21639833. The reversal of 21639828 is 82893612.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21639823) and next prime (21639833).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21639823) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4368 + ... + 7896.

Almost surely, 2^21639828 is an apocalyptic number.

21639828 is a gapful number since it is divisible by the number (28) 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 21639828, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29256640).

21639828 is an abundant number, since it is smaller than the sum of its proper divisors (36873452).

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

21639828 is a wasteful number, since it uses less digits than its factorization.

21639828 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3616 (or 3614 counting only the distinct ones).

The product of its digits is 41472, while the sum is 39.

The square root of 21639828 is about 4651.8628526645. The cubic root of 21639828 is about 278.6663963989. Note that the first 3 decimals are identical.

The spelling of 21639828 in words is "twenty-one million, six hundred thirty-nine thousand, eight hundred twenty-eight".