665640 has 72 divisors (see below), whose sum is σ = 2214810. Its totient is φ = 173376.

The previous prime is 665633. The next prime is 665659. The reversal of 665640 is 46566.

665640 is a `hidden beast` number, since 6 + 656 + 4 + 0 = 666.

It can be written as a sum of positive squares in only one way, i.e., 599076 + 66564 = 774^2 + 258^2 .

It is a tau number, because it is divible by the number of its divisors (72).

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 665640.

It is an unprimeable number.

665640 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 15459 + ... + 15501.

2⁶⁶⁵⁶⁴⁰ is an apocalyptic number.

665640 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 665640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1107405).

665640 is an abundant number, since it is smaller than the sum of its proper divisors (1549170).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

665640 is a wasteful number, since it uses less digits than its factorization.

665640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 103 (or 53 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 27.

The square root of 665640 is about 815.8676363234. The cubic root of 665640 is about 87.3131796369.

The spelling of 665640 in words is "six hundred sixty-five thousand, six hundred forty".