2809 has 3 divisors (see below), whose sum is σ = 2863.
Its totient is φ = 2756.
The previous prime is 2803. The next prime is 2819. The reversal of 2809 is 9082.
2809 = T52 + T53.
The square root of 2809 is 53.
It is a perfect power (a square), and thus also a powerful number.
It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.
It can be written as a sum of positive squares in only one way, i.e., 2025 + 784 = 45^2 + 28^2
It is not a de Polignac number, because 2809 - 23 = 2801 is a prime.
It is an Ulam number.
It is a Duffinian number.
It is a plaindrome in base 7.
It is a nialpdrome in base 15.
It is a zygodrome in base 7.
It is not an unprimeable number, because it can be changed into a prime (2801) by changing a digit.
It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 27 + ... + 79.
22809 is an apocalyptic number.
2809 is the 53-rd square number.
2809 is the 27-th centered octagonal number.
It is an amenable number.
2809 is a deficient number, since it is larger than the sum of its proper divisors (54).
2809 is an frugal number, since it uses more digits than its factorization.
2809 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 106 (or 53 counting only the distinct ones).
The product of its (nonzero) digits is 144, while the sum is 19.
The cubic root of 2809 is about 14.1096826674.
Multiplying 2809 by its product of nonzero digits (144), we get a square (404496 = 6362).
It can be divided in two parts, 280 and 9, that added together give a square (289 = 172).
The spelling of 2809 in words is "two thousand, eight hundred nine".