1666440217 has 6 divisors (see below), whose sum is σ = 1804488702. Its totient is φ = 1538252352.

The previous prime is 1666440199. The next prime is 1666440227. The reversal of 1666440217 is 7120446661.

It can be written as a sum of positive squares in 3 ways, for example, as 61716736 + 1604723481 = 7856^2 + 40059^2 .

It is not a de Polignac number, because 1666440217 - 2²³ = 1658051609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1666440227) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4930128 + ... + 4930465.

It is an arithmetic number, because the mean of its divisors is an integer number (300748117).

Almost surely, 2^1666440217 is an apocalyptic number.

It is an amenable number.

1666440217 is a deficient number, since it is larger than the sum of its proper divisors (138048485).

1666440217 is an equidigital number, since it uses as much as digits as its factorization.

1666440217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9860619 (or 9860606 counting only the distinct ones).

The product of its (nonzero) digits is 48384, while the sum is 37.

The square root of 1666440217 is about 40822.0555214947. The cubic root of 1666440217 is about 1185.5774019110.

Adding to 1666440217 its reverse (7120446661), we get a palindrome (8786886878).

The spelling of 1666440217 in words is "one billion, six hundred sixty-six million, four hundred forty thousand, two hundred seventeen".