666646 has 4 divisors (see below), whose sum is σ = 999972. Its totient is φ = 333322.

The previous prime is 666643. The next prime is 666647. The reversal of 666646 is 646666.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 646666 = 2 ⋅323333.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666643) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 166660 + ... + 166663.

It is an arithmetic number, because the mean of its divisors is an integer number (249993).

2⁶⁶⁶⁶⁴⁶ is an apocalyptic number.

666646 is a deficient number, since it is larger than the sum of its proper divisors (333326).

666646 is a wasteful number, since it uses less digits than its factorization.

666646 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 333325.

The product of its digits is 31104, while the sum is 34.

The square root of 666646 is about 816.4839251326. The cubic root of 666646 is about 87.3571437645.

The spelling of 666646 in words is "six hundred sixty-six thousand, six hundred forty-six".