53991 has 12 divisors (see below), whose sum is σ = 89232. Its totient is φ = 30816.

The previous prime is 53987. The next prime is 53993. The reversal of 53991 is 19935.

It is not a de Polignac number, because 53991 - 2² = 53987 is a prime.

53991 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (53993) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 366 + ... + 491.

It is an arithmetic number, because the mean of its divisors is an integer number (7436).

2⁵³⁹⁹¹ is an apocalyptic number.

53991 is a deficient number, since it is larger than the sum of its proper divisors (35241).

53991 is a wasteful number, since it uses less digits than its factorization.

53991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 870 (or 867 counting only the distinct ones).

The product of its digits is 1215, while the sum is 27.

The square root of 53991 is about 232.3596350488. The cubic root of 53991 is about 37.7955315118.

It can be divided in two parts, 539 and 91, that added together give a triangular number (630 = T₃₅).

The spelling of 53991 in words is "fifty-three thousand, nine hundred ninety-one".