166821817 has 2 divisors, whose sum is σ = 166821818. Its totient is φ = 166821816.

The previous prime is 166821797. The next prime is 166821827. The reversal of 166821817 is 718128661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 112593321 + 54228496 = 10611^2 + 7364^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-166821817 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 166821817.

It is not a weakly prime, because it can be changed into another prime (166821827) 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, 83410908 + 83410909.

It is an arithmetic number, because the mean of its divisors is an integer number (83410909).

Almost surely, 2^166821817 is an apocalyptic number.

It is an amenable number.

166821817 is a deficient number, since it is larger than the sum of its proper divisors (1).

166821817 is an equidigital number, since it uses as much as digits as its factorization.

166821817 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 32256, while the sum is 40.

The square root of 166821817 is about 12915.9520361451. The cubic root of 166821817 is about 550.4919202258.

The spelling of 166821817 in words is "one hundred sixty-six million, eight hundred twenty-one thousand, eight hundred seventeen".