21766364821 has 4 divisors (see below), whose sum is σ = 21774343500. Its totient is φ = 21758386144.

The previous prime is 21766364803. The next prime is 21766364843. The reversal of 21766364821 is 12846366712.

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 19539846225 + 2226518596 = 139785^2 + 47186^2 .

It is a cyclic number.

It is not a de Polignac number, because 21766364821 - 2¹³ = 21766356629 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 (21766364861) 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, 3985246 + ... + 3990703.

It is an arithmetic number, because the mean of its divisors is an integer number (5443585875).

Almost surely, 2^21766364821 is an apocalyptic number.

It is an amenable number.

21766364821 is a deficient number, since it is larger than the sum of its proper divisors (7978679).

21766364821 is an equidigital number, since it uses as much as digits as its factorization.

21766364821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7978678.

The product of its digits is 580608, while the sum is 46.

The spelling of 21766364821 in words is "twenty-one billion, seven hundred sixty-six million, three hundred sixty-four thousand, eight hundred twenty-one".