21684020 has 24 divisors (see below), whose sum is σ = 45645768. Its totient is φ = 8652800.

The previous prime is 21684017. The next prime is 21684023. The reversal of 21684020 is 2048612.

It is an interprime number because it is at equal distance from previous prime (21684017) and next prime (21684023).

It can be written as a sum of positive squares in 4 ways, for example, as 487204 + 21196816 = 698^2 + 4604^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21684023) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9380 + ... + 11460.

It is an arithmetic number, because the mean of its divisors is an integer number (1901907).

Almost surely, 2^21684020 is an apocalyptic number.

21684020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21684020 is an abundant number, since it is smaller than the sum of its proper divisors (23961748).

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

21684020 is a wasteful number, since it uses less digits than its factorization.

21684020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2611 (or 2609 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 23.

The square root of 21684020 is about 4656.6103551833. The cubic root of 21684020 is about 278.8559612441.

The spelling of 21684020 in words is "twenty-one million, six hundred eighty-four thousand, twenty".