166221778321 has 2 divisors, whose sum is σ = 166221778322. Its totient is φ = 166221778320.

The previous prime is 166221778291. The next prime is 166221778351. The reversal of 166221778321 is 123877122661.

166221778321 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a balanced prime because it is at equal distance from previous prime (166221778291) and next prime (166221778351).

It can be written as a sum of positive squares in only one way, i.e., 130108097025 + 36113681296 = 360705^2 + 190036^2 .

It is an emirp because it is prime and its reverse (123877122661) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 166221778321 - 2⁷ = 166221778193 is a prime.

It is not a weakly prime, because it can be changed into another prime (166221778351) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83110889160 + 83110889161.

It is an arithmetic number, because the mean of its divisors is an integer number (83110889161).

Almost surely, 2^166221778321 is an apocalyptic number.

It is an amenable number.

166221778321 is a deficient number, since it is larger than the sum of its proper divisors (1).

166221778321 is an equidigital number, since it uses as much as digits as its factorization.

166221778321 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 338688, while the sum is 46.

The spelling of 166221778321 in words is "one hundred sixty-six billion, two hundred twenty-one million, seven hundred seventy-eight thousand, three hundred twenty-one".