66221391 has 4 divisors (see below), whose sum is σ = 88295192. Its totient is φ = 44147592.

The previous prime is 66221381. The next prime is 66221399. The reversal of 66221391 is 19312266.

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

It is not a de Polignac number, because 66221391 - 2⁵ = 66221359 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 (66221399) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11036896 + ... + 11036901.

It is an arithmetic number, because the mean of its divisors is an integer number (22073798).

Almost surely, 2^66221391 is an apocalyptic number.

66221391 is a deficient number, since it is larger than the sum of its proper divisors (22073801).

66221391 is a wasteful number, since it uses less digits than its factorization.

66221391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22073800.

The product of its digits is 3888, while the sum is 30.

The square root of 66221391 is about 8137.6526713789. The cubic root of 66221391 is about 404.5753634963.

The spelling of 66221391 in words is "sixty-six million, two hundred twenty-one thousand, three hundred ninety-one".