21021021 has 12 divisors (see below), whose sum is σ = 34701472. Its totient is φ = 12011976.

The previous prime is 21021001. The next prime is 21021043. The reversal of 21021021 is 12012012.

It is not a de Polignac number, because 21021021 - 2⁷ = 21020893 is a prime.

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

It is a Duffinian number.

21021021 is a modest number, since divided by 21021 gives 21 as remainder.

It is a junction number, because it is equal to n+sod(n) for n = 21020994 and 21021012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021001) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 166771 + ... + 166896.

Almost surely, 2^21021021 is an apocalyptic number.

21021021 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21021021 is a deficient number, since it is larger than the sum of its proper divisors (13680451).

21021021 is a wasteful number, since it uses less digits than its factorization.

21021021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 333680 (or 333677 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 9.

The square root of 21021021 is about 4584.8687004101. The cubic root of 21021021 is about 275.9844430425.

Adding to 21021021 its reverse (12012012), we get a palindrome (33033033).

Subtracting from 21021021 its reverse (12012012), we obtain a palindrome (9009009).

The spelling of 21021021 in words is "twenty-one million, twenty-one thousand, twenty-one".