166640561 has 2 divisors, whose sum is σ = 166640562. Its totient is φ = 166640560.

The previous prime is 166640501. The next prime is 166640569. The reversal of 166640561 is 165046661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 104939536 + 61701025 = 10244^2 + 7855^2 .

It is a cyclic number.

It is not a de Polignac number, because 166640561 - 2¹⁴ = 166624177 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (166640569) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83320280 + 83320281.

It is an arithmetic number, because the mean of its divisors is an integer number (83320281).

Almost surely, 2^166640561 is an apocalyptic number.

It is an amenable number.

166640561 is a deficient number, since it is larger than the sum of its proper divisors (1).

166640561 is an equidigital number, since it uses as much as digits as its factorization.

166640561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 25920, while the sum is 35.

The square root of 166640561 is about 12908.9333796406. The cubic root of 166640561 is about 550.2924736447.

The spelling of 166640561 in words is "one hundred sixty-six million, six hundred forty thousand, five hundred sixty-one".