163991 has 2 divisors, whose sum is σ = 163992. Its totient is φ = 163990.

The previous prime is 163987. The next prime is 163993. The reversal of 163991 is 199361.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 163991 - 2² = 163987 is a prime.

It is a Sophie Germain prime.

Together with 163993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (163993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 81995 + 81996.

It is an arithmetic number, because the mean of its divisors is an integer number (81996).

2¹⁶³⁹⁹¹ is an apocalyptic number.

163991 is a deficient number, since it is larger than the sum of its proper divisors (1).

163991 is an equidigital number, since it uses as much as digits as its factorization.

163991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1458, while the sum is 29.

The square root of 163991 is about 404.9580225159. The cubic root of 163991 is about 54.7360354424.

The spelling of 163991 in words is "one hundred sixty-three thousand, nine hundred ninety-one".