166393991 has 2 divisors, whose sum is σ = 166393992. Its totient is φ = 166393990.

The previous prime is 166393939. The next prime is 166393999. The reversal of 166393991 is 199393661.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-166393991 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (166393999) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83196995 + 83196996.

It is an arithmetic number, because the mean of its divisors is an integer number (83196996).

Almost surely, 2^166393991 is an apocalyptic number.

166393991 is a deficient number, since it is larger than the sum of its proper divisors (1).

166393991 is an equidigital number, since it uses as much as digits as its factorization.

166393991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 236196, while the sum is 47.

The square root of 166393991 is about 12899.3794811999. The cubic root of 166393991 is about 550.0209259256.

The spelling of 166393991 in words is "one hundred sixty-six million, three hundred ninety-three thousand, nine hundred ninety-one".