21393684 has 72 divisors (see below), whose sum is σ = 61687080. Its totient is φ = 6193152.

The previous prime is 21393683. The next prime is 21393707. The reversal of 21393684 is 48639312.

It can be written as a sum of positive squares in 4 ways, for example, as 49284 + 21344400 = 222^2 + 4620^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21393683) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6612 + ... + 9300.

It is an arithmetic number, because the mean of its divisors is an integer number (856765).

Almost surely, 2^21393684 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 21393684, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30843540).

21393684 is an abundant number, since it is smaller than the sum of its proper divisors (40293396).

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

21393684 is a wasteful number, since it uses less digits than its factorization.

21393684 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2729 (or 2724 counting only the distinct ones).

The product of its digits is 31104, while the sum is 36.

The square root of 21393684 is about 4625.3306908804. The cubic root of 21393684 is about 277.6057936044.

The spelling of 21393684 in words is "twenty-one million, three hundred ninety-three thousand, six hundred eighty-four".