660721321 has 32 divisors (see below), whose sum is σ = 765943808. Its totient is φ = 565470720.

The previous prime is 660721309. The next prime is 660721339. The reversal of 660721321 is 123127066.

It is a cyclic number.

It is not a de Polignac number, because 660721321 - 2¹⁹ = 660197033 is a prime.

It is the 25705-th Hogben number.

It is a self number, because there is not a number n which added to its sum of digits gives 660721321.

It is not an unprimeable number, because it can be changed into a prime (660721301) by changing a digit.

It is a nontrivial repunit in base 25704.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1088200 + ... + 1088806.

It is an arithmetic number, because the mean of its divisors is an integer number (23935744).

Almost surely, 2^660721321 is an apocalyptic number.

660721321 is the 14841-st hex number.

It is an amenable number.

660721321 is a deficient number, since it is larger than the sum of its proper divisors (105222487).

660721321 is a wasteful number, since it uses less digits than its factorization.

660721321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 761.

The product of its (nonzero) digits is 3024, while the sum is 28.

The square root of 660721321 is about 25704.5000145889. The cubic root of 660721321 is about 870.9758377039.

Adding to 660721321 its reverse (123127066), we get a palindrome (783848387).

The spelling of 660721321 in words is "six hundred sixty million, seven hundred twenty-one thousand, three hundred twenty-one".