665621 has 6 divisors (see below), whose sum is σ = 731766. Its totient is φ = 605000.

The previous prime is 665617. The next prime is 665629. The reversal of 665621 is 126566.

It can be written as a sum of positive squares in only one way, i.e., 662596 + 3025 = 814^2 + 55^2 .

It is not a de Polignac number, because 665621 - 2² = 665617 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665629) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 2630 + ... + 2871.

It is an arithmetic number, because the mean of its divisors is an integer number (121961).

2⁶⁶⁵⁶²¹ is an apocalyptic number.

It is an amenable number.

665621 is a deficient number, since it is larger than the sum of its proper divisors (66145).

665621 is a wasteful number, since it uses less digits than its factorization.

665621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5523 (or 5512 counting only the distinct ones).

The product of its digits is 2160, while the sum is 26.

The square root of 665621 is about 815.8559921947. The cubic root of 665621 is about 87.3123488744.

The spelling of 665621 in words is "six hundred sixty-five thousand, six hundred twenty-one".