21013220 has 24 divisors (see below), whose sum is σ = 44298744. Its totient is φ = 8372736.

The previous prime is 21013217. The next prime is 21013249. The reversal of 21013220 is 2231012.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 18496 + 20994724 = 136^2 + 4582^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3644 + ... + 7436.

It is an arithmetic number, because the mean of its divisors is an integer number (1845781).

Almost surely, 2^21013220 is an apocalyptic number.

21013220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21013220 is an abundant number, since it is smaller than the sum of its proper divisors (23285524).

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

21013220 is a wasteful number, since it uses less digits than its factorization.

21013220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4079 (or 4077 counting only the distinct ones).

The product of its (nonzero) digits is 24, while the sum is 11.

The square root of 21013220 is about 4584.0178882723. The cubic root of 21013220 is about 275.9502991091.

Adding to 21013220 its reverse (2231012), we get a palindrome (23244232).

The spelling of 21013220 in words is "twenty-one million, thirteen thousand, two hundred twenty".