305991 has 16 divisors (see below), whose sum is σ = 518400. Its totient is φ = 174744.

The previous prime is 305971. The next prime is 305999. The reversal of 305991 is 199503.

It is not a de Polignac number, because 305991 - 2⁶ = 305927 is a prime.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

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

305991 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (305999) 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, 621 + ... + 998.

It is an arithmetic number, because the mean of its divisors is an integer number (32400).

2³⁰⁵⁹⁹¹ is an apocalyptic number.

305991 is a deficient number, since it is larger than the sum of its proper divisors (212409).

305991 is a wasteful number, since it uses less digits than its factorization.

305991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1635 (or 1629 counting only the distinct ones).

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

The square root of 305991 is about 553.1645324856. The cubic root of 305991 is about 67.3859803482.

It can be divided in two parts, 305 and 991, that added together give a 4-th power (1296 = 6⁴).

The spelling of 305991 in words is "three hundred five thousand, nine hundred ninety-one".