21100120021 has 4 divisors (see below), whose sum is σ = 21100759200. Its totient is φ = 21099480844.

The previous prime is 21100120003. The next prime is 21100120031. The reversal of 21100120021 is 12002100112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21100120021 - 2⁷ = 21100119893 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21100120001) 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, 267211 + ... + 337048.

It is an arithmetic number, because the mean of its divisors is an integer number (5275189800).

Almost surely, 2^21100120021 is an apocalyptic number.

It is an amenable number.

21100120021 is a deficient number, since it is larger than the sum of its proper divisors (639179).

21100120021 is an equidigital number, since it uses as much as digits as its factorization.

21100120021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 639178.

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

Adding to 21100120021 its reverse (12002100112), we get a palindrome (33102220133).

The spelling of 21100120021 in words is "twenty-one billion, one hundred million, one hundred twenty thousand, twenty-one".