20621121821 has 4 divisors (see below), whose sum is σ = 20642229372. Its totient is φ = 20600014272.

The previous prime is 20621121721. The next prime is 20621121869. The reversal of 20621121821 is 12812112602.

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 10015005625 + 10606116196 = 100075^2 + 102986^2 .

It is a cyclic number.

It is not a de Polignac number, because 20621121821 - 2¹⁴ = 20621105437 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 (20621121721) 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, 10552310 + ... + 10554263.

It is an arithmetic number, because the mean of its divisors is an integer number (5160557343).

Almost surely, 2^20621121821 is an apocalyptic number.

It is an amenable number.

20621121821 is a deficient number, since it is larger than the sum of its proper divisors (21107551).

20621121821 is an equidigital number, since it uses as much as digits as its factorization.

20621121821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21107550.

The product of its (nonzero) digits is 768, while the sum is 26.

The spelling of 20621121821 in words is "twenty billion, six hundred twenty-one million, one hundred twenty-one thousand, eight hundred twenty-one".