521665 has 8 divisors (see below), whose sum is σ = 632808. Its totient is φ = 412800.

The previous prime is 521659. The next prime is 521669. The reversal of 521665 is 566125.

It can be written as a sum of positive squares in 4 ways, for example, as 327184 + 194481 = 572^2 + 441^2 .

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

It is not a de Polignac number, because 521665 - 2³ = 521657 is a prime.

It is a Duffinian number.

521665 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (521669) 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, 12 + ... + 1021.

It is an arithmetic number, because the mean of its divisors is an integer number (79101).

2⁵²¹⁶⁶⁵ is an apocalyptic number.

It is an amenable number.

521665 is a deficient number, since it is larger than the sum of its proper divisors (111143).

521665 is a wasteful number, since it uses less digits than its factorization.

521665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1139.

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

The square root of 521665 is about 722.2638022219. The cubic root of 521665 is about 80.5002507611.

The spelling of 521665 in words is "five hundred twenty-one thousand, six hundred sixty-five".