667878921 has 6 divisors (see below), whose sum is σ = 964714010. Its totient is φ = 445252608.

The previous prime is 667878901. The next prime is 667878931. The reversal of 667878921 is 129878766.

It can be written as a sum of positive squares in only one way, i.e., 574273296 + 93605625 = 23964^2 + 9675^2 .

It is not a de Polignac number, because 667878921 - 2⁷ = 667878793 is a prime.

It is a super-2 number, since 2×667878921² = 892124506232248482, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (667878901) 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, 37104376 + ... + 37104393.

Almost surely, 2^667878921 is an apocalyptic number.

It is an amenable number.

667878921 is a deficient number, since it is larger than the sum of its proper divisors (296835089).

667878921 is a wasteful number, since it uses less digits than its factorization.

667878921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 74208775 (or 74208772 counting only the distinct ones).

The product of its digits is 2032128, while the sum is 54.

The square root of 667878921 is about 25843.3535169103. The cubic root of 667878921 is about 874.1096449672.

The spelling of 667878921 in words is "six hundred sixty-seven million, eight hundred seventy-eight thousand, nine hundred twenty-one".