665869 has 4 divisors (see below), whose sum is σ = 688860. Its totient is φ = 642880.

The previous prime is 665857. The next prime is 665897. The reversal of 665869 is 968566.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 968566 = 2 ⋅484283.

It can be written as a sum of positive squares in 2 ways, for example, as 405769 + 260100 = 637^2 + 510^2 .

It is a cyclic number.

It is not a de Polignac number, because 665869 - 2¹¹ = 663821 is a prime.

It is a super-2 number, since 2×665869² = 886763050322, which contains 22 as substring.

It is a Duffinian number.

665869 is a lucky number.

It is a nialpdrome in base 7.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665069) 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, 11452 + ... + 11509.

It is an arithmetic number, because the mean of its divisors is an integer number (172215).

2⁶⁶⁵⁸⁶⁹ is an apocalyptic number.

It is an amenable number.

665869 is a deficient number, since it is larger than the sum of its proper divisors (22991).

665869 is a wasteful number, since it uses less digits than its factorization.

665869 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22990.

The product of its digits is 77760, while the sum is 40.

The square root of 665869 is about 816.0079656474. The cubic root of 665869 is about 87.3231912676.

The spelling of 665869 in words is "six hundred sixty-five thousand, eight hundred sixty-nine".