21243684 has 96 divisors (see below), whose sum is σ = 62770176. Its totient is φ = 5431680.

The previous prime is 21243683. The next prime is 21243707. The reversal of 21243684 is 48634212.

It is not an unprimeable number, because it can be changed into a prime (21243683) 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, 76554 + ... + 76830.

It is an arithmetic number, because the mean of its divisors is an integer number (653856).

Almost surely, 2^21243684 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 21243684, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31385088).

21243684 is an abundant number, since it is smaller than the sum of its proper divisors (41526492).

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

21243684 is a wasteful number, since it uses less digits than its factorization.

21243684 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 385 (or 383 counting only the distinct ones).

The product of its digits is 9216, while the sum is 30.

The square root of 21243684 is about 4609.0871113486. The cubic root of 21243684 is about 276.9554681722.

Adding to 21243684 its reverse (48634212), we get a palindrome (69877896).

The spelling of 21243684 in words is "twenty-one million, two hundred forty-three thousand, six hundred eighty-four".