166666721 has 16 divisors (see below), whose sum is σ = 183355200. Its totient is φ = 150562368.

The previous prime is 166666711. The next prime is 166666723. The reversal of 166666721 is 127666661.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-166666721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (166666723) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 155375 + ... + 156443.

It is an arithmetic number, because the mean of its divisors is an integer number (11459700).

Almost surely, 2^166666721 is an apocalyptic number.

It is an amenable number.

166666721 is a deficient number, since it is larger than the sum of its proper divisors (16688479).

166666721 is a wasteful number, since it uses less digits than its factorization.

166666721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1328.

The product of its digits is 108864, while the sum is 41.

The square root of 166666721 is about 12909.9465916788. The cubic root of 166666721 is about 550.3212679507.

The spelling of 166666721 in words is "one hundred sixty-six million, six hundred sixty-six thousand, seven hundred twenty-one".