659664721 has 4 divisors (see below), whose sum is σ = 659726500. Its totient is φ = 659602944.

The previous prime is 659664713. The next prime is 659664809. The reversal of 659664721 is 127466956.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 132503121 + 527161600 = 11511^2 + 22960^2 .

It is a cyclic number.

It is not a de Polignac number, because 659664721 - 2³ = 659664713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (659661721) 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, 10296 + ... + 37753.

It is an arithmetic number, because the mean of its divisors is an integer number (164931625).

Almost surely, 2^659664721 is an apocalyptic number.

659664721 is the 13729-th nonagonal number.

It is an amenable number.

659664721 is a deficient number, since it is larger than the sum of its proper divisors (61779).

659664721 is a wasteful number, since it uses less digits than its factorization.

659664721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 61778.

The product of its digits is 544320, while the sum is 46.

The square root of 659664721 is about 25683.9389697141. The cubic root of 659664721 is about 870.5113130335.

It can be divided in two parts, 6596 and 64721, that added together give a palindrome (71317).

The spelling of 659664721 in words is "six hundred fifty-nine million, six hundred sixty-four thousand, seven hundred twenty-one".