21100220021 has 4 divisors (see below), whose sum is σ = 22341409452. Its totient is φ = 19859030592.

The previous prime is 21100220003. The next prime is 21100220023. The reversal of 21100220021 is 12002200112.

It is a happy number.

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 17925460996 + 3174759025 = 133886^2 + 56345^2 .

It is a cyclic number.

It is not a de Polignac number, because 21100220021 - 2²⁶ = 21033111157 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21100219984 and 21100220011.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21100220023) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 620594690 + ... + 620594723.

It is an arithmetic number, because the mean of its divisors is an integer number (5585352363).

Almost surely, 2^21100220021 is an apocalyptic number.

It is an amenable number.

21100220021 is a deficient number, since it is larger than the sum of its proper divisors (1241189431).

21100220021 is a wasteful number, since it uses less digits than its factorization.

21100220021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1241189430.

The product of its (nonzero) digits is 16, while the sum is 11.

Adding to 21100220021 its reverse (12002200112), we get a palindrome (33102420133).

The spelling of 21100220021 in words is "twenty-one billion, one hundred million, two hundred twenty thousand, twenty-one".