665881 has 8 divisors (see below), whose sum is σ = 693000. Its totient is φ = 639360.

The previous prime is 665857. The next prime is 665897. The reversal of 665881 is 188566.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 25 + 665856 = 5^2 + 816^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 665881 - 2⁹ = 665369 is a prime.

It is a super-2 number, since 2×665881² = 886795012322, which contains 22 as substring.

It is a Duffinian number.

665881 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (665801) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4395 + ... + 4543.

It is an arithmetic number, because the mean of its divisors is an integer number (86625).

2⁶⁶⁵⁸⁸¹ is an apocalyptic number.

It is an amenable number.

665881 is a deficient number, since it is larger than the sum of its proper divisors (27119).

665881 is a wasteful number, since it uses less digits than its factorization.

665881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 299.

The product of its digits is 11520, while the sum is 34.

The square root of 665881 is about 816.0153184837. The cubic root of 665881 is about 87.3237158313.

The spelling of 665881 in words is "six hundred sixty-five thousand, eight hundred eighty-one".