166221778091 has 2 divisors, whose sum is σ = 166221778092. Its totient is φ = 166221778090.

The previous prime is 166221778057. The next prime is 166221778111. The reversal of 166221778091 is 190877122661.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 166221778091 - 2³⁴ = 149041908907 is a prime.

It is not a weakly prime, because it can be changed into another prime (166221778291) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83110889045 + 83110889046.

It is an arithmetic number, because the mean of its divisors is an integer number (83110889046).

Almost surely, 2^166221778091 is an apocalyptic number.

166221778091 is a deficient number, since it is larger than the sum of its proper divisors (1).

166221778091 is an equidigital number, since it uses as much as digits as its factorization.

166221778091 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 508032, while the sum is 50.

The spelling of 166221778091 in words is "one hundred sixty-six billion, two hundred twenty-one million, seven hundred seventy-eight thousand, ninety-one".