66720439809 has 27 divisors (see below), whose sum is σ = 99845432713. Its totient is φ = 42932025024.

The previous prime is 66720439789. The next prime is 66720439813. The reversal of 66720439809 is 90893402766.

It is a happy number.

The square root of 66720439809 is 258303.

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

66720439809 is a `hidden beast` number, since 66 + 72 + 0 + 439 + 80 + 9 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 26584324209 + 40136115600 = 163047^2 + 200340^2 .

It is not a de Polignac number, because 66720439809 - 2²⁹ = 66183568897 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66720439829) 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, 22470877 + ... + 22473845.

Almost surely, 2^66720439809 is an apocalyptic number.

66720439809 is the 258303-rd square number.

66720439809 is the 129152-nd centered octagonal number.

It is an amenable number.

66720439809 is a deficient number, since it is larger than the sum of its proper divisors (33124992904).

66720439809 is an frugal number, since it uses more digits than its factorization.

66720439809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6002 (or 3001 counting only the distinct ones).

The product of its (nonzero) digits is 3919104, while the sum is 54.

The spelling of 66720439809 in words is "sixty-six billion, seven hundred twenty million, four hundred thirty-nine thousand, eight hundred nine".