103991 has 2 divisors, whose sum is σ = 103992. Its totient is φ = 103990.

The previous prime is 103981. The next prime is 103993. The reversal of 103991 is 199301.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 103991 - 2¹⁰ = 102967 is a prime.

Together with 103993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (103993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 51995 + 51996.

It is an arithmetic number, because the mean of its divisors is an integer number (51996).

2¹⁰³⁹⁹¹ is an apocalyptic number.

103991 is a deficient number, since it is larger than the sum of its proper divisors (1).

103991 is an equidigital number, since it uses as much as digits as its factorization.

103991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 243, while the sum is 23.

The square root of 103991 is about 322.4763557224. The cubic root of 103991 is about 47.0253371760.

It can be divided in two parts, 1039 and 91, that multiplied together give a palindrome (94549).

The spelling of 103991 in words is "one hundred three thousand, nine hundred ninety-one".