21780224 has 36 divisors (see below), whose sum is σ = 43843800. Its totient is φ = 10798080.

The previous prime is 21780217. The next prime is 21780229. The reversal of 21780224 is 42208712.

It is a zygodrome in base 3.

It is a junction number, because it is equal to n+sod(n) for n = 21780193 and 21780202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21780229) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 37859 + ... + 38429.

Almost surely, 2^21780224 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 21780224, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21921900).

21780224 is an abundant number, since it is smaller than the sum of its proper divisors (22063576).

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

21780224 is an equidigital number, since it uses as much as digits as its factorization.

21780224 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 736 (or 722 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 26.

The square root of 21780224 is about 4666.9287545451. The cubic root of 21780224 is about 279.2677465507.

Adding to 21780224 its reverse (42208712), we get a palindrome (63988936).

The spelling of 21780224 in words is "twenty-one million, seven hundred eighty thousand, two hundred twenty-four".