166811221 has 2 divisors, whose sum is σ = 166811222. Its totient is φ = 166811220.

The previous prime is 166811189. The next prime is 166811243. The reversal of 166811221 is 122118661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 87796900 + 79014321 = 9370^2 + 8889^2 .

It is a cyclic number.

It is not a de Polignac number, because 166811221 - 2⁵ = 166811189 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 166811221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (166811291) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83405610 + 83405611.

It is an arithmetic number, because the mean of its divisors is an integer number (83405611).

Almost surely, 2^166811221 is an apocalyptic number.

It is an amenable number.

166811221 is a deficient number, since it is larger than the sum of its proper divisors (1).

166811221 is an equidigital number, since it uses as much as digits as its factorization.

166811221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1152, while the sum is 28.

The square root of 166811221 is about 12915.5418391951. The cubic root of 166811221 is about 550.4802648040.

Adding to 166811221 its reverse (122118661), we get a palindrome (288929882).

The spelling of 166811221 in words is "one hundred sixty-six million, eight hundred eleven thousand, two hundred twenty-one".