166666691 has 4 divisors (see below), whose sum is σ = 176470632. Its totient is φ = 156862752.

The previous prime is 166666673. The next prime is 166666693. The reversal of 166666691 is 196666661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 196666661 = 29 ⋅6781609.

It is a cyclic number.

It is not a de Polignac number, because 166666691 - 2⁶ = 166666627 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (166666693) 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, 4901945 + ... + 4901978.

It is an arithmetic number, because the mean of its divisors is an integer number (44117658).

Almost surely, 2^166666691 is an apocalyptic number.

166666691 is a deficient number, since it is larger than the sum of its proper divisors (9803941).

166666691 is an equidigital number, since it uses as much as digits as its factorization.

166666691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9803940.

The product of its digits is 419904, while the sum is 47.

The square root of 166666691 is about 12909.9454297840. The cubic root of 166666691 is about 550.3212349314.

The spelling of 166666691 in words is "one hundred sixty-six million, six hundred sixty-six thousand, six hundred ninety-one".