166278991 has 2 divisors, whose sum is σ = 166278992. Its totient is φ = 166278990.

The previous prime is 166278943. The next prime is 166279021. The reversal of 166278991 is 199872661.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 166278991 - 2¹⁹ = 165754703 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (166278901) 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, 83139495 + 83139496.

It is an arithmetic number, because the mean of its divisors is an integer number (83139496).

Almost surely, 2^166278991 is an apocalyptic number.

166278991 is a deficient number, since it is larger than the sum of its proper divisors (1).

166278991 is an equidigital number, since it uses as much as digits as its factorization.

166278991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 326592, while the sum is 49.

The square root of 166278991 is about 12894.9211319806. The cubic root of 166278991 is about 549.8941846020.

The spelling of 166278991 in words is "one hundred sixty-six million, two hundred seventy-eight thousand, nine hundred ninety-one".