21021020 has 12 divisors (see below), whose sum is σ = 44144184. Its totient is φ = 8408400.

The previous prime is 21021001. The next prime is 21021043. The reversal of 21021020 is 2012012.

It is a junction number, because it is equal to n+sod(n) for n = 21020989 and 21021007.

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, 525506 + ... + 525545.

It is an arithmetic number, because the mean of its divisors is an integer number (3678682).

Almost surely, 2^21021020 is an apocalyptic number.

21021020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21021020 is an abundant number, since it is smaller than the sum of its proper divisors (23123164).

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

21021020 is a wasteful number, since it uses less digits than its factorization.

21021020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1051060 (or 1051058 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 8.

The square root of 21021020 is about 4584.8685913557. The cubic root of 21021020 is about 275.9844386662.

Adding to 21021020 its reverse (2012012), we get a palindrome (23033032).

The spelling of 21021020 in words is "twenty-one million, twenty-one thousand, twenty".