66618217 has 4 divisors (see below), whose sum is σ = 66655876. Its totient is φ = 66580560.

The previous prime is 66618203. The next prime is 66618221. The reversal of 66618217 is 71281666.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 71281666 = 2 ⋅35640833.

It can be written as a sum of positive squares in 2 ways, for example, as 1590121 + 65028096 = 1261^2 + 8064^2 .

It is a cyclic number.

It is not a de Polignac number, because 66618217 - 2⁷ = 66618089 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66618247) 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, 16038 + ... + 19759.

It is an arithmetic number, because the mean of its divisors is an integer number (16663969).

Almost surely, 2^66618217 is an apocalyptic number.

It is an amenable number.

66618217 is a deficient number, since it is larger than the sum of its proper divisors (37659).

66618217 is a wasteful number, since it uses less digits than its factorization.

66618217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 37658.

The product of its digits is 24192, while the sum is 37.

The square root of 66618217 is about 8161.9983459935. The cubic root of 66618217 is about 405.3818823469.

It can be divided in two parts, 6661 and 8217, that added together give a triangular number (14878 = T₁₇₂).

The spelling of 66618217 in words is "sixty-six million, six hundred eighteen thousand, two hundred seventeen".