165549991 has 2 divisors, whose sum is σ = 165549992. Its totient is φ = 165549990.

The previous prime is 165549977. The next prime is 165550001. The reversal of 165549991 is 199945561.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 165549991 - 2²³ = 157161383 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (165549931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 82774995 + 82774996.

It is an arithmetic number, because the mean of its divisors is an integer number (82774996).

Almost surely, 2^165549991 is an apocalyptic number.

165549991 is a deficient number, since it is larger than the sum of its proper divisors (1).

165549991 is an equidigital number, since it uses as much as digits as its factorization.

165549991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 437400, while the sum is 49.

The square root of 165549991 is about 12866.6231389592. The cubic root of 165549991 is about 549.0893923578.

The spelling of 165549991 in words is "one hundred sixty-five million, five hundred forty-nine thousand, nine hundred ninety-one".