665680 has 40 divisors (see below), whose sum is σ = 1586952. Its totient is φ = 259584.

The previous prime is 665677. The next prime is 665713. The reversal of 665680 is 86566.

It can be written as a sum of positive squares in 4 ways, for example, as 69696 + 595984 = 264^2 + 772^2 .

It is a tau number, because it is divible by the number of its divisors (40).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4162 + ... + 4318.

2⁶⁶⁵⁶⁸⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 665680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (793476).

665680 is an abundant number, since it is smaller than the sum of its proper divisors (921272).

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

665680 is a wasteful number, since it uses less digits than its factorization.

665680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 223 (or 217 counting only the distinct ones).

The product of its (nonzero) digits is 8640, while the sum is 31.

The square root of 665680 is about 815.8921497355. The cubic root of 665680 is about 87.3149285589.

The spelling of 665680 in words is "six hundred sixty-five thousand, six hundred eighty".