21205766884 has 27 divisors (see below), whose sum is σ = 39430653577. Its totient is φ = 9976854464.

The previous prime is 21205766839. The next prime is 21205766887. The reversal of 21205766884 is 48866750212.

The square root of 21205766884 is 145622.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 16509680100 + 4696086784 = 128490^2 + 68528^2 .

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21205766887) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 4949007 + ... + 4953289.

Almost surely, 2^21205766884 is an apocalyptic number.

21205766884 is the 145622-nd square number.

It is an amenable number.

21205766884 is a deficient number, since it is larger than the sum of its proper divisors (18224886693).

21205766884 is an frugal number, since it uses more digits than its factorization.

21205766884 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8604 (or 4302 counting only the distinct ones).

The product of its (nonzero) digits is 1290240, while the sum is 49.

Multiplying 21205766884 by its sum of digits (49), we get a square (1039082577316 = 1019354²).

The spelling of 21205766884 in words is "twenty-one billion, two hundred five million, seven hundred sixty-six thousand, eight hundred eighty-four".