165556561 has 2 divisors, whose sum is σ = 165556562. Its totient is φ = 165556560.

The previous prime is 165556511. The next prime is 165556583. The reversal of 165556561 is 165655561.

165556561 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 can be written as a sum of positive squares in only one way, i.e., 124992400 + 40564161 = 11180^2 + 6369^2 .

It is a cyclic number.

It is not a de Polignac number, because 165556561 - 2¹¹ = 165554513 is a prime.

It is not a weakly prime, because it can be changed into another prime (165556511) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 82778280 + 82778281.

It is an arithmetic number, because the mean of its divisors is an integer number (82778281).

Almost surely, 2^165556561 is an apocalyptic number.

It is an amenable number.

165556561 is a deficient number, since it is larger than the sum of its proper divisors (1).

165556561 is an equidigital number, since it uses as much as digits as its factorization.

165556561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 135000, while the sum is 40.

The square root of 165556561 is about 12866.8784481707. The cubic root of 165556561 is about 549.0966559635.

The spelling of 165556561 in words is "one hundred sixty-five million, five hundred fifty-six thousand, five hundred sixty-one".