165991291 has 2 divisors, whose sum is σ = 165991292. Its totient is φ = 165991290.

The previous prime is 165991289. The next prime is 165991303. The reversal of 165991291 is 192199561.

It is a weak prime.

It is an emirp because it is prime and its reverse (192199561) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 165991291 - 2¹ = 165991289 is a prime.

Together with 165991289, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (165991261) 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, 82995645 + 82995646.

It is an arithmetic number, because the mean of its divisors is an integer number (82995646).

Almost surely, 2^165991291 is an apocalyptic number.

165991291 is a deficient number, since it is larger than the sum of its proper divisors (1).

165991291 is an equidigital number, since it uses as much as digits as its factorization.

165991291 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 43740, while the sum is 43.

The square root of 165991291 is about 12883.7607475457. The cubic root of 165991291 is about 549.5768546998.

The spelling of 165991291 in words is "one hundred sixty-five million, nine hundred ninety-one thousand, two hundred ninety-one".