21668723209 has 27 divisors (see below), whose sum is σ = 26798091093. Its totient is φ = 17466519168.

The previous prime is 21668723207. The next prime is 21668723213. The reversal of 21668723209 is 90232786612.

The square root of 21668723209 is 147203.

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

It can be written as a sum of positive squares in 4 ways, for example, as 6178431609 + 15490291600 = 78603^2 + 124460^2 .

It is not a de Polignac number, because 21668723209 - 2¹ = 21668723207 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21668723207) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 17516539 + ... + 17517775.

Almost surely, 2^21668723209 is an apocalyptic number.

21668723209 is the 147203-rd square number.

21668723209 is the 73602-nd centered octagonal number.

It is an amenable number.

21668723209 is a deficient number, since it is larger than the sum of its proper divisors (5129367884).

21668723209 is an frugal number, since it uses more digits than its factorization.

21668723209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2522 (or 1261 counting only the distinct ones).

The product of its (nonzero) digits is 435456, while the sum is 46.

The spelling of 21668723209 in words is "twenty-one billion, six hundred sixty-eight million, seven hundred twenty-three thousand, two hundred nine".