21205166305 has 4 divisors (see below), whose sum is σ = 25446199572. Its totient is φ = 16964133040.

The previous prime is 21205166287. The next prime is 21205166309. The reversal of 21205166305 is 50366150212.

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 8549591296 + 12655575009 = 92464^2 + 112497^2 .

It is not a de Polignac number, because 21205166305 - 2¹³ = 21205158113 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21205166309) 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, 2120516626 + ... + 2120516635.

It is an arithmetic number, because the mean of its divisors is an integer number (6361549893).

Almost surely, 2^21205166305 is an apocalyptic number.

It is an amenable number.

21205166305 is a deficient number, since it is larger than the sum of its proper divisors (4241033267).

21205166305 is an equidigital number, since it uses as much as digits as its factorization.

21205166305 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4241033266.

The product of its (nonzero) digits is 10800, while the sum is 31.

The spelling of 21205166305 in words is "twenty-one billion, two hundred five million, one hundred sixty-six thousand, three hundred five".