665581 has 4 divisors (see below), whose sum is σ = 760672. Its totient is φ = 570492.

The previous prime is 665573. The next prime is 665591. The reversal of 665581 is 185566.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 665581 - 2³ = 665573 is a prime.

It is a super-2 number, since 2×665581² = 885996135122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665501) 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, 47535 + ... + 47548.

It is an arithmetic number, because the mean of its divisors is an integer number (190168).

2⁶⁶⁵⁵⁸¹ is an apocalyptic number.

It is an amenable number.

665581 is a deficient number, since it is larger than the sum of its proper divisors (95091).

665581 is an equidigital number, since it uses as much as digits as its factorization.

665581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 95090.

The product of its digits is 7200, while the sum is 31.

The square root of 665581 is about 815.8314776962. The cubic root of 665581 is about 87.3105998491.

The spelling of 665581 in words is "six hundred sixty-five thousand, five hundred eighty-one".