21331020 has 24 divisors (see below), whose sum is σ = 59727024. Its totient is φ = 5688256.

The previous prime is 21331001. The next prime is 21331021. The reversal of 21331020 is 2013312.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (12).

It is a junction number, because it is equal to n+sod(n) for n = 21330987 and 21331005.

It is not an unprimeable number, because it can be changed into a prime (21331021) 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, 177699 + ... + 177818.

It is an arithmetic number, because the mean of its divisors is an integer number (2488626).

Almost surely, 2^21331020 is an apocalyptic number.

21331020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21331020 is an abundant number, since it is smaller than the sum of its proper divisors (38396004).

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

21331020 is a wasteful number, since it uses less digits than its factorization.

21331020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 355529 (or 355527 counting only the distinct ones).

The product of its (nonzero) digits is 36, while the sum is 12.

The square root of 21331020 is about 4618.5517210485. The cubic root of 21331020 is about 277.3344845295.

Adding to 21331020 its reverse (2013312), we get a palindrome (23344332).

The spelling of 21331020 in words is "twenty-one million, three hundred thirty-one thousand, twenty".