165817991 has 2 divisors, whose sum is σ = 165817992. Its totient is φ = 165817990.

The previous prime is 165817963. The next prime is 165818011. The reversal of 165817991 is 199718561.

165817991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 165817991 - 2¹⁰ = 165816967 is a prime.

It is a super-2 number, since 2×165817991² = 54991212278552162, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (165817291) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 82908995 + 82908996.

It is an arithmetic number, because the mean of its divisors is an integer number (82908996).

Almost surely, 2^165817991 is an apocalyptic number.

165817991 is a deficient number, since it is larger than the sum of its proper divisors (1).

165817991 is an equidigital number, since it uses as much as digits as its factorization.

165817991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 136080, while the sum is 47.

The square root of 165817991 is about 12877.0334704854. The cubic root of 165817991 is about 549.3855297360.

The spelling of 165817991 in words is "one hundred sixty-five million, eight hundred seventeen thousand, nine hundred ninety-one".