21243220 has 24 divisors (see below), whose sum is σ = 44942184. Its totient is φ = 8434176.

The previous prime is 21243193. The next prime is 21243227. The reversal of 21243220 is 2234212.

It can be written as a sum of positive squares in 4 ways, for example, as 9326916 + 11916304 = 3054^2 + 3452^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21243194 and 21243203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21243227) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1137 + ... + 6616.

It is an arithmetic number, because the mean of its divisors is an integer number (1872591).

Almost surely, 2^21243220 is an apocalyptic number.

21243220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21243220 is an abundant number, since it is smaller than the sum of its proper divisors (23698964).

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

21243220 is a wasteful number, since it uses less digits than its factorization.

21243220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7899 (or 7897 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 16.

The square root of 21243220 is about 4609.0367757266. The cubic root of 21243220 is about 276.9534517568.

Adding to 21243220 its reverse (2234212), we get a palindrome (23477432).

The spelling of 21243220 in words is "twenty-one million, two hundred forty-three thousand, two hundred twenty".