21031020 has 72 divisors (see below), whose sum is σ = 65869440. Its totient is φ = 5425920.

The previous prime is 21031019. The next prime is 21031027. The reversal of 21031020 is 2013012.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a junction number, because it is equal to n+sod(n) for n = 21030993 and 21031011.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21031027) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3696 + ... + 7464.

Almost surely, 2^21031020 is an apocalyptic number.

21031020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21031020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32934720).

21031020 is an abundant number, since it is smaller than the sum of its proper divisors (44838420).

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

21031020 is a wasteful number, since it uses less digits than its factorization.

21031020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3815 (or 3810 counting only the distinct ones).

The product of its (nonzero) digits is 12, while the sum is 9.

The square root of 21031020 is about 4585.9590054862. The cubic root of 21031020 is about 276.0281949772.

Adding to 21031020 its reverse (2013012), we get a palindrome (23044032).

The spelling of 21031020 in words is "twenty-one million, thirty-one thousand, twenty".