665521 has 8 divisors (see below), whose sum is σ = 703080. Its totient is φ = 628992.

The previous prime is 665507. The next prime is 665527. The reversal of 665521 is 125566.

665521 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 4 ways, for example, as 57121 + 608400 = 239^2 + 780^2 .

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 665521 - 2¹⁹ = 141233 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (665527) 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, 1321 + ... + 1753.

It is an arithmetic number, because the mean of its divisors is an integer number (87885).

2⁶⁶⁵⁵²¹ is an apocalyptic number.

It is an amenable number.

665521 is a deficient number, since it is larger than the sum of its proper divisors (37559).

665521 is a wasteful number, since it uses less digits than its factorization.

665521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 515.

The product of its digits is 1800, while the sum is 25.

The square root of 665521 is about 815.7947045673. The cubic root of 665521 is about 87.3079761798.

The spelling of 665521 in words is "six hundred sixty-five thousand, five hundred twenty-one".