21684212 has 48 divisors (see below), whose sum is σ = 43213632. Its totient is φ = 9434880.

The previous prime is 21684209. The next prime is 21684217. The reversal of 21684212 is 21248612.

It is a happy number.

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, 138038 + ... + 138194.

It is an arithmetic number, because the mean of its divisors is an integer number (900284).

Almost surely, 2^21684212 is an apocalyptic number.

21684212 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

21684212 is a deficient number, since it is larger than the sum of its proper divisors (21529420).

21684212 is a wasteful number, since it uses less digits than its factorization.

21684212 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 288 (or 286 counting only the distinct ones).

The product of its digits is 1536, while the sum is 26.

The square root of 21684212 is about 4656.6309709918. The cubic root of 21684212 is about 278.8567842801.

Subtracting from 21684212 its reverse (21248612), we obtain a square (435600 = 660²).

The spelling of 21684212 in words is "twenty-one million, six hundred eighty-four thousand, two hundred twelve".