21761657221 has 4 divisors (see below), whose sum is σ = 21778541100. Its totient is φ = 21744773344.

The previous prime is 21761657209. The next prime is 21761657227. The reversal of 21761657221 is 12275616712.

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 19443234721 + 2318422500 = 139439^2 + 48150^2 .

It is a cyclic number.

It is not a de Polignac number, because 21761657221 - 2¹⁵ = 21761624453 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 (21761657227) 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, 8440006 + ... + 8442583.

It is an arithmetic number, because the mean of its divisors is an integer number (5444635275).

Almost surely, 2^21761657221 is an apocalyptic number.

It is an amenable number.

21761657221 is a deficient number, since it is larger than the sum of its proper divisors (16883879).

21761657221 is a wasteful number, since it uses less digits than its factorization.

21761657221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16883878.

The product of its digits is 70560, while the sum is 40.

The spelling of 21761657221 in words is "twenty-one billion, seven hundred sixty-one million, six hundred fifty-seven thousand, two hundred twenty-one".