660721 has 6 divisors (see below), whose sum is σ = 691250. Its totient is φ = 631488.

The previous prime is 660719. The next prime is 660727. The reversal of 660721 is 127066.

It can be written as a sum of positive squares in only one way, i.e., 541696 + 119025 = 736^2 + 345^2 .

It is not a de Polignac number, because 660721 - 2¹ = 660719 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 660692 and 660701.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (660727) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 96 + ... + 1153.

2⁶⁶⁰⁷²¹ is an apocalyptic number.

It is an amenable number.

660721 is a deficient number, since it is larger than the sum of its proper divisors (30529).

660721 is a wasteful number, since it uses less digits than its factorization.

660721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1295 (or 1272 counting only the distinct ones).

The product of its (nonzero) digits is 504, while the sum is 22.

The square root of 660721 is about 812.8474641653. The cubic root of 660721 is about 87.0975696654.

Adding to 660721 its reverse (127066), we get a palindrome (787787).

The spelling of 660721 in words is "six hundred sixty thousand, seven hundred twenty-one".