166781 has 2 divisors, whose sum is σ = 166782. Its totient is φ = 166780.

The previous prime is 166741. The next prime is 166783. The reversal of 166781 is 187661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 111556 + 55225 = 334^2 + 235^2 .

It is an emirp because it is prime and its reverse (187661) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-166781 is a prime.

It is a super-2 number, since 2×166781² = 55631803922, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 166783, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a plaindrome in base 14.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (166783) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83390 + 83391.

It is an arithmetic number, because the mean of its divisors is an integer number (83391).

2¹⁶⁶⁷⁸¹ is an apocalyptic number.

It is an amenable number.

166781 is a deficient number, since it is larger than the sum of its proper divisors (1).

166781 is an equidigital number, since it uses as much as digits as its factorization.

166781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 29.

The square root of 166781 is about 408.3882956207. The cubic root of 166781 is about 55.0447019501.

The spelling of 166781 in words is "one hundred sixty-six thousand, seven hundred eighty-one".