21002001021 has 24 divisors (see below), whose sum is σ = 30881760000. Its totient is φ = 13750031232.

The previous prime is 21002000989. The next prime is 21002001043. The reversal of 21002001021 is 12010020012.

It is not a de Polignac number, because 21002001021 - 2⁵ = 21002000989 is a prime.

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

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21002000994 and 21002001012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21002001091) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 516180 + ... + 555378.

It is an arithmetic number, because the mean of its divisors is an integer number (1286740000).

Almost surely, 2^21002001021 is an apocalyptic number.

It is an amenable number.

21002001021 is a deficient number, since it is larger than the sum of its proper divisors (9879758979).

21002001021 is a wasteful number, since it uses less digits than its factorization.

21002001021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40273 (or 40270 counting only the distinct ones).

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

Adding to 21002001021 its reverse (12010020012), we get a palindrome (33012021033).

The spelling of 21002001021 in words is "twenty-one billion, two million, one thousand, twenty-one".