21684738 has 64 divisors (see below), whose sum is σ = 48263040. Its totient is φ = 6469632.

The previous prime is 21684713. The next prime is 21684739. The reversal of 21684738 is 83748612.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21684696 and 21684705.

It is not an unprimeable number, because it can be changed into a prime (21684739) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 223506 + ... + 223602.

It is an arithmetic number, because the mean of its divisors is an integer number (754110).

Almost surely, 2^21684738 is an apocalyptic number.

21684738 is an abundant number, since it is smaller than the sum of its proper divisors (26578302).

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

21684738 is a wasteful number, since it uses less digits than its factorization.

21684738 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 211.

The product of its digits is 64512, while the sum is 39.

The square root of 21684738 is about 4656.6874492497. The cubic root of 21684738 is about 278.8590390309.

It can be divided in two parts, 21684 and 738, that added together give a palindrome (22422).

The spelling of 21684738 in words is "twenty-one million, six hundred eighty-four thousand, seven hundred thirty-eight".