21261620221 has 4 divisors (see below), whose sum is σ = 21262229244. Its totient is φ = 21261011200.

The previous prime is 21261620147. The next prime is 21261620243. The reversal of 21261620221 is 12202616212.

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 3754625625 + 17506994596 = 61275^2 + 132314^2 .

It is a cyclic number.

It is not a de Polignac number, because 21261620221 - 2²¹ = 21259523069 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 (21261620021) 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, 248740 + ... + 323101.

It is an arithmetic number, because the mean of its divisors is an integer number (5315557311).

Almost surely, 2^21261620221 is an apocalyptic number.

It is an amenable number.

21261620221 is a deficient number, since it is larger than the sum of its proper divisors (609023).

21261620221 is an equidigital number, since it uses as much as digits as its factorization.

21261620221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 609022.

The product of its (nonzero) digits is 1152, while the sum is 25.

The spelling of 21261620221 in words is "twenty-one billion, two hundred sixty-one million, six hundred twenty thousand, two hundred twenty-one".