21031220 has 24 divisors (see below), whose sum is σ = 50475264. Its totient is φ = 7210656.

The previous prime is 21031217. The next prime is 21031229. The reversal of 21031220 is 2213012.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21031229) 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, 74972 + ... + 75251.

It is an arithmetic number, because the mean of its divisors is an integer number (2103136).

Almost surely, 2^21031220 is an apocalyptic number.

21031220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21031220 is an abundant number, since it is smaller than the sum of its proper divisors (29444044).

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

21031220 is a wasteful number, since it uses less digits than its factorization.

21031220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 150239 (or 150237 counting only the distinct ones).

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

The square root of 21031220 is about 4585.9808111243. The cubic root of 21031220 is about 276.0290699619.

Adding to 21031220 its reverse (2213012), we get a palindrome (23244232).

The spelling of 21031220 in words is "twenty-one million, thirty-one thousand, two hundred twenty".