66312221 has 4 divisors (see below), whose sum is σ = 66920700. Its totient is φ = 65703744.

The previous prime is 66312199. The next prime is 66312271. The reversal of 66312221 is 12221366.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12221366 = 2 ⋅6110683.

It can be written as a sum of positive squares in 2 ways, for example, as 56040196 + 10272025 = 7486^2 + 3205^2 .

It is a cyclic number.

It is not a de Polignac number, because 66312221 - 2⁶ = 66312157 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 (66312271) 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, 304076 + ... + 304293.

It is an arithmetic number, because the mean of its divisors is an integer number (16730175).

Almost surely, 2^66312221 is an apocalyptic number.

It is an amenable number.

66312221 is a deficient number, since it is larger than the sum of its proper divisors (608479).

66312221 is a wasteful number, since it uses less digits than its factorization.

66312221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 608478.

The product of its digits is 864, while the sum is 23.

The square root of 66312221 is about 8143.2316066780. The cubic root of 66312221 is about 404.7602523536.

Adding to 66312221 its reverse (12221366), we get a palindrome (78533587).

The spelling of 66312221 in words is "sixty-six million, three hundred twelve thousand, two hundred twenty-one".