166999991 has 2 divisors, whose sum is σ = 166999992. Its totient is φ = 166999990.

The previous prime is 166999969. The next prime is 167000039. The reversal of 166999991 is 199999661.

It is a weak prime.

It is an emirp because it is prime and its reverse (199999661) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 166999991 - 2⁶ = 166999927 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 166999991.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (166999961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83499995 + 83499996.

It is an arithmetic number, because the mean of its divisors is an integer number (83499996).

Almost surely, 2^166999991 is an apocalyptic number.

166999991 is a deficient number, since it is larger than the sum of its proper divisors (1).

166999991 is an equidigital number, since it uses as much as digits as its factorization.

166999991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2125764, while the sum is 59.

The square root of 166999991 is about 12922.8476350996. The cubic root of 166999991 is about 550.6878347461.

It can be divided in two parts, 16 and 6999991, that added together give a palindrome (7000007).

The spelling of 166999991 in words is "one hundred sixty-six million, nine hundred ninety-nine thousand, nine hundred ninety-one".