668666 has 4 divisors (see below), whose sum is σ = 1003002. Its totient is φ = 334332.

The previous prime is 668623. The next prime is 668671. The reversal of 668666 is 666866.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 666866 = 2 ⋅333433.

It can be written as a sum of positive squares in only one way, i.e., 616225 + 52441 = 785^2 + 229^2 .

It is a super-2 number, since 2×668666² = 894228439112, which contains 22 as substring.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 167165 + ... + 167168.

2⁶⁶⁸⁶⁶⁶ is an apocalyptic number.

668666 is a deficient number, since it is larger than the sum of its proper divisors (334336).

668666 is a wasteful number, since it uses less digits than its factorization.

668666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 334335.

The product of its digits is 62208, while the sum is 38.

The square root of 668666 is about 817.7200009783. The cubic root of 668666 is about 87.4452882461.

The spelling of 668666 in words is "six hundred sixty-eight thousand, six hundred sixty-six".