21231220 has 12 divisors (see below), whose sum is σ = 44585604. Its totient is φ = 8492480.

The previous prime is 21231173. The next prime is 21231241. The reversal of 21231220 is 2213212.

It can be written as a sum of positive squares in 2 ways, for example, as 5817744 + 15413476 = 2412^2 + 3926^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21231220.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 530761 + ... + 530800.

It is an arithmetic number, because the mean of its divisors is an integer number (3715467).

Almost surely, 2^21231220 is an apocalyptic number.

21231220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21231220 is an abundant number, since it is smaller than the sum of its proper divisors (23354384).

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

21231220 is a wasteful number, since it uses less digits than its factorization.

21231220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1061570 (or 1061568 counting only the distinct ones).

The product of its (nonzero) digits is 48, while the sum is 13.

The square root of 21231220 is about 4607.7348013965. The cubic root of 21231220 is about 276.9012928812.

Adding to 21231220 its reverse (2213212), we get a palindrome (23444432).

The spelling of 21231220 in words is "twenty-one million, two hundred thirty-one thousand, two hundred twenty".