166812821 has 4 divisors (see below), whose sum is σ = 190643232. Its totient is φ = 142982412.

The previous prime is 166812803. The next prime is 166812839. The reversal of 166812821 is 128218661.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 128218661 = 433 ⋅296117.

It is an interprime number because it is at equal distance from previous prime (166812803) and next prime (166812839).

It is a cyclic number.

It is not a de Polignac number, because 166812821 - 2⁶ = 166812757 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (166812851) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11915195 + ... + 11915208.

It is an arithmetic number, because the mean of its divisors is an integer number (47660808).

Almost surely, 2^166812821 is an apocalyptic number.

It is an amenable number.

166812821 is a deficient number, since it is larger than the sum of its proper divisors (23830411).

166812821 is an equidigital number, since it uses as much as digits as its factorization.

166812821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23830410.

The product of its digits is 9216, while the sum is 35.

The square root of 166812821 is about 12915.6037799245. The cubic root of 166812821 is about 550.4820248088.

The spelling of 166812821 in words is "one hundred sixty-six million, eight hundred twelve thousand, eight hundred twenty-one".