166809991 has 2 divisors, whose sum is σ = 166809992. Its totient is φ = 166809990.

The previous prime is 166809983. The next prime is 166810013. The reversal of 166809991 is 199908661.

166809991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 166809991 - 2³ = 166809983 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (166809901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83404995 + 83404996.

It is an arithmetic number, because the mean of its divisors is an integer number (83404996).

Almost surely, 2^166809991 is an apocalyptic number.

166809991 is a deficient number, since it is larger than the sum of its proper divisors (1).

166809991 is an equidigital number, since it uses as much as digits as its factorization.

166809991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 209952, while the sum is 49.

The square root of 166809991 is about 12915.4942220575. The cubic root of 166809991 is about 550.4789117928.

The spelling of 166809991 in words is "one hundred sixty-six million, eight hundred nine thousand, nine hundred ninety-one".