665640749 has 4 divisors (see below), whose sum is σ = 665964540. Its totient is φ = 665316960.

The previous prime is 665640719. The next prime is 665640751. The reversal of 665640749 is 947046566.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 55204900 + 610435849 = 7430^2 + 24707^2 .

It is a cyclic number.

It is not a de Polignac number, because 665640749 - 2¹⁶ = 665575213 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665640719) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 158792 + ... + 162929.

It is an arithmetic number, because the mean of its divisors is an integer number (166491135).

Almost surely, 2^665640749 is an apocalyptic number.

It is an amenable number.

665640749 is a deficient number, since it is larger than the sum of its proper divisors (323791).

665640749 is a wasteful number, since it uses less digits than its factorization.

665640749 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 323790.

The product of its (nonzero) digits is 1088640, while the sum is 47.

The square root of 665640749 is about 25800.0145154998. The cubic root of 665640749 is about 873.1321238612.

The spelling of 665640749 in words is "six hundred sixty-five million, six hundred forty thousand, seven hundred forty-nine".