105991 has 4 divisors (see below), whose sum is σ = 107352. Its totient is φ = 104632.

The previous prime is 105983. The next prime is 105997. The reversal of 105991 is 199501.

105991 = T₃ + T₄ + ... + T₈₅.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 105991 - 2³ = 105983 is a prime.

It is a super-2 number, since 2×105991² = 22468184162, which contains 22 as substring.

It is a Duffinian number.

It is a zygodrome in base 2.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (105997) 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, 556 + ... + 721.

It is an arithmetic number, because the mean of its divisors is an integer number (26838).

2¹⁰⁵⁹⁹¹ is an apocalyptic number.

105991 is a deficient number, since it is larger than the sum of its proper divisors (1361).

105991 is an equidigital number, since it uses as much as digits as its factorization.

105991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1360.

The product of its (nonzero) digits is 405, while the sum is 25.

The square root of 105991 is about 325.5625899885. The cubic root of 105991 is about 47.3248954520.

It can be divided in two parts, 1059 and 91, that multiplied together give a palindrome (96369).

The spelling of 105991 in words is "one hundred five thousand, nine hundred ninety-one".