21563724 has 144 divisors (see below), whose sum is σ = 65587200. Its totient is φ = 5503680.

The previous prime is 21563723. The next prime is 21563753. The reversal of 21563724 is 42736512.

Its product of digits (10080) is a multiple of the sum of its prime divisors (56).

It is a junction number, because it is equal to n+sod(n) for n = 21563691 and 21563700.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21563723) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 695589 + ... + 695619.

Almost surely, 2^21563724 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 21563724, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32793600).

21563724 is an abundant number, since it is smaller than the sum of its proper divisors (44023476).

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

21563724 is a wasteful number, since it uses less digits than its factorization.

21563724 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 85 (or 56 counting only the distinct ones).

The product of its digits is 10080, while the sum is 30.

The square root of 21563724 is about 4643.6756992710. The cubic root of 21563724 is about 278.3393368453.

The spelling of 21563724 in words is "twenty-one million, five hundred sixty-three thousand, seven hundred twenty-four".