21684216 has 64 divisors (see below), whose sum is σ = 57150720. Its totient is φ = 6842880.

The previous prime is 21684209. The next prime is 21684217. The reversal of 21684216 is 61248612.

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21684217) 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, 89856 + ... + 90096.

It is an arithmetic number, because the mean of its divisors is an integer number (892980).

Almost surely, 2^21684216 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21684216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28575360).

21684216 is an abundant number, since it is smaller than the sum of its proper divisors (35466504).

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

21684216 is a wasteful number, since it uses less digits than its factorization.

21684216 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 436 (or 432 counting only the distinct ones).

The product of its digits is 4608, while the sum is 30.

The square root of 21684216 is about 4656.6314004868. The cubic root of 21684216 is about 278.8568014266.

The spelling of 21684216 in words is "twenty-one million, six hundred eighty-four thousand, two hundred sixteen".