66172221 has 10 divisors (see below), whose sum is σ = 98849982. Its totient is φ = 44114760.

The previous prime is 66172189. The next prime is 66172261. The reversal of 66172221 is 12227166.

66172221 is a `hidden beast` number, since 6 + 617 + 22 + 21 = 666.

It can be written as a sum of positive squares in only one way, i.e., 56475225 + 9696996 = 7515^2 + 3114^2 .

It is not a de Polignac number, because 66172221 - 2⁵ = 66172189 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66172261) 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 9 ways as a sum of consecutive naturals, for example, 408390 + ... + 408551.

Almost surely, 2^66172221 is an apocalyptic number.

It is an amenable number.

66172221 is a deficient number, since it is larger than the sum of its proper divisors (32677761).

66172221 is an equidigital number, since it uses as much as digits as its factorization.

66172221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 816953 (or 816944 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 66172221 is about 8134.6309688885. The cubic root of 66172221 is about 404.4752050433.

Adding to 66172221 its reverse (12227166), we get a palindrome (78399387).

The spelling of 66172221 in words is "sixty-six million, one hundred seventy-two thousand, two hundred twenty-one".