66399 has 4 divisors (see below), whose sum is σ = 88536. Its totient is φ = 44264.

The previous prime is 66383. The next prime is 66403. The reversal of 66399 is 99366.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 66399 - 2⁴ = 66383 is a prime.

It is an Ulam number.

It is a D-number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66359) 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, 11064 + ... + 11069.

It is an arithmetic number, because the mean of its divisors is an integer number (22134).

2⁶⁶³⁹⁹ is an apocalyptic number.

66399 is a deficient number, since it is larger than the sum of its proper divisors (22137).

66399 is a wasteful number, since it uses less digits than its factorization.

66399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22136.

The product of its digits is 8748, while the sum is 33.

The square root of 66399 is about 257.6800341509. The cubic root of 66399 is about 40.4936737566.

Subtracting from 66399 its sum of digits (33), we obtain a palindrome (66366).

It can be divided in two parts, 66 and 399, that added together give a triangular number (465 = T₃₀).

The spelling of 66399 in words is "sixty-six thousand, three hundred ninety-nine".