66816 has 54 divisors (see below), whose sum is σ = 199290. Its totient is φ = 21504.

The previous prime is 66809. The next prime is 66821. The reversal of 66816 is 61866.

It can be written as a sum of positive squares in only one way, i.e., 57600 + 9216 = 240^2 + 96^2 .

It is a nude number because it is divisible by every one of its digits.

It is a self number, because there is not a number n which added to its sum of digits gives 66816.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 66816.

It is an unprimeable number.

66816 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (3) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 2290 + ... + 2318.

2⁶⁶⁸¹⁶ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 66816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (99645).

66816 is an abundant number, since it is smaller than the sum of its proper divisors (132474).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

66816 is a wasteful number, since it uses less digits than its factorization.

66816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51 (or 34 counting only the distinct ones).

The product of its digits is 1728, while the sum is 27.

The square root of 66816 is about 258.4879107425. The cubic root of 66816 is about 40.5782665759.

Subtracting from 66816 its reverse (61866), we obtain a triangular number (4950 = T₉₉).

The spelling of 66816 in words is "sixty-six thousand, eight hundred sixteen".