551991 has 16 divisors (see below), whose sum is σ = 823680. Its totient is φ = 325920.

The previous prime is 551981. The next prime is 552001. The reversal of 551991 is 199155.

551991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (551981) and next prime (552001).

It is not a de Polignac number, because 551991 - 2⁵ = 551959 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (551911) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1225 + ... + 1613.

It is an arithmetic number, because the mean of its divisors is an integer number (51480).

2⁵⁵¹⁹⁹¹ is an apocalyptic number.

551991 is a deficient number, since it is larger than the sum of its proper divisors (271689).

551991 is a wasteful number, since it uses less digits than its factorization.

551991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 446.

The product of its digits is 2025, while the sum is 30.

The square root of 551991 is about 742.9609680192. The cubic root of 551991 is about 82.0308727692.

Subtracting from 551991 its reverse (199155), we obtain a square (352836 = 594²).

The spelling of 551991 in words is "five hundred fifty-one thousand, nine hundred ninety-one".