549991 has 4 divisors (see below), whose sum is σ = 592312. Its totient is φ = 507672.

The previous prime is 549979. The next prime is 550007. The reversal of 549991 is 199945.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199945 = 5 ⋅39989.

It is a cyclic number.

It is not a de Polignac number, because 549991 - 2⁷ = 549863 is a prime.

It is a Duffinian number.

549991 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 549991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (549911) 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, 21141 + ... + 21166.

It is an arithmetic number, because the mean of its divisors is an integer number (148078).

2⁵⁴⁹⁹⁹¹ is an apocalyptic number.

549991 is a deficient number, since it is larger than the sum of its proper divisors (42321).

549991 is a wasteful number, since it uses less digits than its factorization.

549991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42320.

The product of its digits is 14580, while the sum is 37.

The square root of 549991 is about 741.6137808860. The cubic root of 549991 is about 81.9316801551.

It can be divided in two parts, 549 and 991, that added together give a triangular number (1540 = T₅₅).

The spelling of 549991 in words is "five hundred forty-nine thousand, nine hundred ninety-one".