21002100021 has 24 divisors (see below), whose sum is σ = 34674793920. Its totient is φ = 11999586816.

The previous prime is 21002100011. The next prime is 21002100029. The reversal of 21002100021 is 12000120012.

It is not a de Polignac number, because 21002100021 - 2¹³ = 21002091829 is a prime.

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

It is a junction number, because it is equal to n+sod(n) for n = 21002099976 and 21002100012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21002100029) 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, 575701 + ... + 611093.

It is an arithmetic number, because the mean of its divisors is an integer number (1444783080).

Almost surely, 2^21002100021 is an apocalyptic number.

21002100021 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21002100021 is a deficient number, since it is larger than the sum of its proper divisors (13672693899).

21002100021 is a wasteful number, since it uses less digits than its factorization.

21002100021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44825 (or 44822 counting only the distinct ones).

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

Adding to 21002100021 its reverse (12000120012), we get a palindrome (33002220033).

The spelling of 21002100021 in words is "twenty-one billion, two million, one hundred thousand, twenty-one".