66391 has 4 divisors (see below), whose sum is σ = 71512. Its totient is φ = 61272.

The previous prime is 66383. The next prime is 66403. The reversal of 66391 is 19366.

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 66391 - 2³ = 66383 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 (66301) 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, 2541 + ... + 2566.

It is an arithmetic number, because the mean of its divisors is an integer number (17878).

2⁶⁶³⁹¹ is an apocalyptic number.

66391 is a deficient number, since it is larger than the sum of its proper divisors (5121).

66391 is a wasteful number, since it uses less digits than its factorization.

66391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5120.

The product of its digits is 972, while the sum is 25.

The square root of 66391 is about 257.6645105559. The cubic root of 66391 is about 40.4920474148.

Subtracting from 66391 its sum of digits (25), we obtain a palindrome (66366).

The spelling of 66391 in words is "sixty-six thousand, three hundred ninety-one".