55809 has 20 divisors (see below), whose sum is σ = 91476. Its totient is φ = 33696.

The previous prime is 55807. The next prime is 55813. The reversal of 55809 is 90855.

It can be written as a sum of positive squares in 2 ways, for example, as 23409 + 32400 = 153^2 + 180^2 .

It is not a de Polignac number, because 55809 - 2¹ = 55807 is a prime.

It is a super-2 number, since 2×55809² = 6229288962, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

55809 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (55807) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 1027 + ... + 1079.

It is a Proth number, since it is equal to 109 ⋅ 2⁹ + 1 and 109 < 2⁹.

2⁵⁵⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

55809 is a deficient number, since it is larger than the sum of its proper divisors (35667).

55809 is a wasteful number, since it uses less digits than its factorization.

55809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 78 (or 69 counting only the distinct ones).

The product of its (nonzero) digits is 1800, while the sum is 27.

The square root of 55809 is about 236.2392854713. The cubic root of 55809 is about 38.2150776988.

The spelling of 55809 in words is "fifty-five thousand, eight hundred nine".