21002021 has 8 divisors (see below), whose sum is σ = 22570560. Its totient is φ = 19470528.

The previous prime is 21001991. The next prime is 21002039. The reversal of 21002021 is 12020012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21002021 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21002081) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8081 + ... + 10358.

It is an arithmetic number, because the mean of its divisors is an integer number (2821320).

Almost surely, 2^21002021 is an apocalyptic number.

It is an amenable number.

21002021 is a deficient number, since it is larger than the sum of its proper divisors (1568539).

21002021 is a wasteful number, since it uses less digits than its factorization.

21002021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18523.

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

The square root of 21002021 is about 4582.7961988288. The cubic root of 21002021 is about 275.9012678078.

Adding to 21002021 its reverse (12020012), we get a palindrome (33022033).

Subtracting from 21002021 its reverse (12020012), we obtain a square (8982009 = 2997²).

The spelling of 21002021 in words is "twenty-one million, two thousand, twenty-one".