491809 has 4 divisors (see below), whose sum is σ = 513216. Its totient is φ = 470404.

The previous prime is 491797. The next prime is 491819. The reversal of 491809 is 908194.

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 491809 - 2⁹ = 491297 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 14.

It is not an unprimeable number, because it can be changed into a prime (491819) 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, 10669 + ... + 10714.

It is an arithmetic number, because the mean of its divisors is an integer number (128304).

2⁴⁹¹⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

491809 is a deficient number, since it is larger than the sum of its proper divisors (21407).

491809 is a wasteful number, since it uses less digits than its factorization.

491809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21406.

The product of its (nonzero) digits is 2592, while the sum is 31.

The square root of 491809 is about 701.2909524584. The cubic root of 491809 is about 78.9342506938.

It can be divided in two parts, 4 and 91809, that multiplied together give a square (367236 = 606²).

The spelling of 491809 in words is "four hundred ninety-one thousand, eight hundred nine".