16509 has 4 divisors (see below), whose sum is σ = 22016. Its totient is φ = 11004.

The previous prime is 16493. The next prime is 16519. The reversal of 16509 is 90561.

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, and also an emirpimes, since its reverse is a distinct semiprime: 90561 = 3 ⋅30187.

It is not a de Polignac number, because 16509 - 2⁴ = 16493 is a prime.

It is a D-number.

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

It is a Duffinian number.

It is a plaindrome in base 11.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16519) 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 3 ways as a sum of consecutive naturals, for example, 2749 + ... + 2754.

It is an arithmetic number, because the mean of its divisors is an integer number (5504).

2¹⁶⁵⁰⁹ is an apocalyptic number.

It is an amenable number.

16509 is a deficient number, since it is larger than the sum of its proper divisors (5507).

16509 is an equidigital number, since it uses as much as digits as its factorization.

16509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5506.

The product of its (nonzero) digits is 270, while the sum is 21.

The square root of 16509 is about 128.4873534633. The cubic root of 16509 is about 25.4628447737.

It can be divided in two parts, 16 and 509, that added together give a palindrome (525).

The spelling of 16509 in words is "sixteen thousand, five hundred nine".