166816821 has 4 divisors (see below), whose sum is σ = 222422432. Its totient is φ = 111211212.

The previous prime is 166816813. The next prime is 166816877. The reversal of 166816821 is 128618661.

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: 128618661 = 3 ⋅42872887.

It is not a de Polignac number, because 166816821 - 2³ = 166816813 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 166816821.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (166816721) 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, 27802801 + ... + 27802806.

It is an arithmetic number, because the mean of its divisors is an integer number (55605608).

Almost surely, 2^166816821 is an apocalyptic number.

It is an amenable number.

166816821 is a deficient number, since it is larger than the sum of its proper divisors (55605611).

166816821 is an equidigital number, since it uses as much as digits as its factorization.

166816821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55605610.

The product of its digits is 27648, while the sum is 39.

The square root of 166816821 is about 12915.7586304483. The cubic root of 166816821 is about 550.4864247713.

The spelling of 166816821 in words is "one hundred sixty-six million, eight hundred sixteen thousand, eight hundred twenty-one".