521661 has 8 divisors (see below), whose sum is σ = 794944. Its totient is φ = 298080.

The previous prime is 521659. The next prime is 521669. The reversal of 521661 is 166125.

It is a happy number.

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

It is not a de Polignac number, because 521661 - 2¹ = 521659 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21), and also a Moran number because the ratio is a prime number: 24841 = 521661 / (5 + 2 + 1 + 6 + 6 + 1).

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 521661.

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, 12400 + ... + 12441.

It is an arithmetic number, because the mean of its divisors is an integer number (99368).

2⁵²¹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

521661 is a deficient number, since it is larger than the sum of its proper divisors (273283).

521661 is a wasteful number, since it uses less digits than its factorization.

521661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24851.

The product of its digits is 360, while the sum is 21.

The square root of 521661 is about 722.2610331452. The cubic root of 521661 is about 80.5000450085.

Adding to 521661 its reverse (166125), we get a palindrome (687786).

The spelling of 521661 in words is "five hundred twenty-one thousand, six hundred sixty-one".