165521509 has 2 divisors, whose sum is σ = 165521510. Its totient is φ = 165521508.

The previous prime is 165521507. The next prime is 165521539. The reversal of 165521509 is 905125561.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 165045409 + 476100 = 12847^2 + 690^2 .

It is a cyclic number.

It is not a de Polignac number, because 165521509 - 2¹ = 165521507 is a prime.

Together with 165521507, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (165521507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 82760754 + 82760755.

It is an arithmetic number, because the mean of its divisors is an integer number (82760755).

Almost surely, 2^165521509 is an apocalyptic number.

It is an amenable number.

165521509 is a deficient number, since it is larger than the sum of its proper divisors (1).

165521509 is an equidigital number, since it uses as much as digits as its factorization.

165521509 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 13500, while the sum is 34.

The square root of 165521509 is about 12865.5162741337. The cubic root of 165521509 is about 549.0579012436.

The spelling of 165521509 in words is "one hundred sixty-five million, five hundred twenty-one thousand, five hundred nine".