667688921 has 4 divisors (see below), whose sum is σ = 667740852. Its totient is φ = 667636992.

The previous prime is 667688893. The next prime is 667688929. The reversal of 667688921 is 129886766.

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 495685696 + 172003225 = 22264^2 + 13115^2 .

It is a cyclic number.

It is not a de Polignac number, because 667688921 - 2¹⁸ = 667426777 is a prime.

It is a super-2 number, since 2×667688921² = 891616990452288482, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (667688929) 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, 9161 + ... + 37673.

It is an arithmetic number, because the mean of its divisors is an integer number (166935213).

Almost surely, 2^667688921 is an apocalyptic number.

It is an amenable number.

667688921 is a deficient number, since it is larger than the sum of its proper divisors (51931).

667688921 is a wasteful number, since it uses less digits than its factorization.

667688921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51930.

The product of its digits is 1741824, while the sum is 53.

The square root of 667688921 is about 25839.6772619164. The cubic root of 667688921 is about 874.0267474146.

The spelling of 667688921 in words is "six hundred sixty-seven million, six hundred eighty-eight thousand, nine hundred twenty-one".