16521 has 4 divisors (see below), whose sum is σ = 22032. Its totient is φ = 11012.

The previous prime is 16519. The next prime is 16529. The reversal of 16521 is 12561.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 16521 - 2¹ = 16519 is a prime.

It is a D-number.

It is an alternating number because its digits alternate between odd and even.

16521 is a lucky number.

It is a plaindrome in base 11.

It is a nialpdrome in base 7.

It is a zygodrome in base 7.

It is a self number, because there is not a number n which added to its sum of digits gives 16521.

It is not an unprimeable number, because it can be changed into a prime (16529) 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, 2751 + ... + 2756.

It is an arithmetic number, because the mean of its divisors is an integer number (5508).

2¹⁶⁵²¹ is an apocalyptic number.

It is an amenable number.

16521 is a deficient number, since it is larger than the sum of its proper divisors (5511).

16521 is an equidigital number, since it uses as much as digits as its factorization.

16521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5510.

The product of its digits is 60, while the sum is 15.

The square root of 16521 is about 128.5340421834. The cubic root of 16521 is about 25.4690127252.

Subtracting from 16521 its product of digits (60), we obtain a palindrome (16461).

It can be divided in two parts, 1652 and 1, that added together give a triangular number (1653 = T₅₇).

The spelling of 16521 in words is "sixteen thousand, five hundred twenty-one".