667721 has 4 divisors (see below), whose sum is σ = 672132. Its totient is φ = 663312.

The previous prime is 667699. The next prime is 667727. The reversal of 667721 is 127766.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 126025 + 541696 = 355^2 + 736^2 .

It is a cyclic number.

It is not a de Polignac number, because 667721 - 2⁶ = 667657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (667727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1970 + ... + 2283.

It is an arithmetic number, because the mean of its divisors is an integer number (168033).

2⁶⁶⁷⁷²¹ is an apocalyptic number.

It is an amenable number.

667721 is a deficient number, since it is larger than the sum of its proper divisors (4411).

667721 is a wasteful number, since it uses less digits than its factorization.

667721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4410.

The product of its digits is 3528, while the sum is 29.

The square root of 667721 is about 817.1419705290. The cubic root of 667721 is about 87.4040744679.

The spelling of 667721 in words is "six hundred sixty-seven thousand, seven hundred twenty-one".