21001002021 has 6 divisors (see below), whose sum is σ = 30334780710. Its totient is φ = 14000668008.

The previous prime is 21001002019. The next prime is 21001002041. The reversal of 21001002021 is 12020010012.

It can be written as a sum of positive squares in only one way, i.e., 19569212100 + 1431789921 = 139890^2 + 37839^2 .

It is not a de Polignac number, because 21001002021 - 2¹ = 21001002019 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9), and also a Moran number because the ratio is a prime number: 2333444669 = 21001002021 / (2 + 1 + 0 + 0 + 1 + 0 + 0 + 2 + 0 + 2 + 1).

It is a junction number, because it is equal to n+sod(n) for n = 21001001994 and 21001002012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001002041) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1166722326 + ... + 1166722343.

It is an arithmetic number, because the mean of its divisors is an integer number (5055796785).

Almost surely, 2^21001002021 is an apocalyptic number.

It is an amenable number.

21001002021 is a deficient number, since it is larger than the sum of its proper divisors (9333778689).

21001002021 is a wasteful number, since it uses less digits than its factorization.

21001002021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2333444675 (or 2333444672 counting only the distinct ones).

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

Adding to 21001002021 its reverse (12020010012), we get a palindrome (33021012033).

The spelling of 21001002021 in words is "twenty-one billion, one million, two thousand, twenty-one".