21102100021 has 4 divisors (see below), whose sum is σ = 21189660844. Its totient is φ = 21014539200.

The previous prime is 21102100001. The next prime is 21102100081. The reversal of 21102100021 is 12000120112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11661840100 + 9440259921 = 107990^2 + 97161^2 .

It is a cyclic number.

It is not a de Polignac number, because 21102100021 - 2⁵ = 21102099989 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21102099980 and 21102100007.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21102100001) 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 3 ways as a sum of consecutive naturals, for example, 43780050 + ... + 43780531.

It is an arithmetic number, because the mean of its divisors is an integer number (5297415211).

Almost surely, 2^21102100021 is an apocalyptic number.

It is an amenable number.

21102100021 is a deficient number, since it is larger than the sum of its proper divisors (87560823).

21102100021 is an equidigital number, since it uses as much as digits as its factorization.

21102100021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 87560822.

The product of its (nonzero) digits is 8, while the sum is 10.

Adding to 21102100021 its reverse (12000120112), we get a palindrome (33102220133).

The spelling of 21102100021 in words is "twenty-one billion, one hundred two million, one hundred thousand, twenty-one".