66109661 has 4 divisors (see below), whose sum is σ = 66553500. Its totient is φ = 65665824.

The previous prime is 66109643. The next prime is 66109679. The reversal of 66109661 is 16690166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 16690166 = 2 ⋅8345083.

It is an interprime number because it is at equal distance from previous prime (66109643) and next prime (66109679).

It can be written as a sum of positive squares in 2 ways, for example, as 4972900 + 61136761 = 2230^2 + 7819^2 .

It is a cyclic number.

It is not a de Polignac number, because 66109661 - 2¹⁴ = 66093277 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 (66109601) 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, 221696 + ... + 221993.

It is an arithmetic number, because the mean of its divisors is an integer number (16638375).

Almost surely, 2^66109661 is an apocalyptic number.

It is an amenable number.

66109661 is a deficient number, since it is larger than the sum of its proper divisors (443839).

66109661 is a wasteful number, since it uses less digits than its factorization.

66109661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 443838.

The product of its (nonzero) digits is 11664, while the sum is 35.

The square root of 66109661 is about 8130.7847714719. The cubic root of 66109661 is about 404.3476996397.

The spelling of 66109661 in words is "sixty-six million, one hundred nine thousand, six hundred sixty-one".