166181221 has 2 divisors, whose sum is σ = 166181222. Its totient is φ = 166181220.

The previous prime is 166181219. The next prime is 166181363. The reversal of 166181221 is 122181661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 154008100 + 12173121 = 12410^2 + 3489^2 .

It is a cyclic number.

It is not a de Polignac number, because 166181221 - 2¹ = 166181219 is a prime.

Together with 166181219, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 166181221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (166181621) 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, 83090610 + 83090611.

It is an arithmetic number, because the mean of its divisors is an integer number (83090611).

Almost surely, 2^166181221 is an apocalyptic number.

It is an amenable number.

166181221 is a deficient number, since it is larger than the sum of its proper divisors (1).

166181221 is an equidigital number, since it uses as much as digits as its factorization.

166181221 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 166181221 is about 12891.1295470956. The cubic root of 166181221 is about 549.7863864672.

The spelling of 166181221 in words is "one hundred sixty-six million, one hundred eighty-one thousand, two hundred twenty-one".