165205805521 has 2 divisors, whose sum is σ = 165205805522. Its totient is φ = 165205805520.

The previous prime is 165205805491. The next prime is 165205805549. The reversal of 165205805521 is 125508502561.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 143959536400 + 21246269121 = 379420^2 + 145761^2 .

It is a cyclic number.

It is not a de Polignac number, because 165205805521 - 2¹⁷ = 165205674449 is a prime.

It is not a weakly prime, because it can be changed into another prime (165205805561) 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, 82602902760 + 82602902761.

It is an arithmetic number, because the mean of its divisors is an integer number (82602902761).

Almost surely, 2^165205805521 is an apocalyptic number.

It is an amenable number.

165205805521 is a deficient number, since it is larger than the sum of its proper divisors (1).

165205805521 is an equidigital number, since it uses as much as digits as its factorization.

165205805521 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 120000, while the sum is 40.

The spelling of 165205805521 in words is "one hundred sixty-five billion, two hundred five million, eight hundred five thousand, five hundred twenty-one".