18691 has 2 divisors, whose sum is σ = 18692.
Its totient is φ = 18690.
The previous prime is 18679. The next prime is 18701. The reversal of 18691 is 19681.
Subtracting 18691 from its reverse (19681), we obtain a triangular number (990 = T44).
It is a strong prime.
It is an emirp because it is prime and its reverse (19681) is a distict prime.
It is a cyclic number.
It is not a de Polignac number, because 18691 - 213 = 10499 is a prime.
It is a nialpdrome in base 12.
It is not a weakly prime, because it can be changed into another prime (18661) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (5) of ones.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9345 + 9346.
It is an arithmetic number, because the mean of its divisors is an integer number (9346).
218691 is an apocalyptic number.
18691 is a deficient number, since it is larger than the sum of its proper divisors (1).
18691 is an equidigital number, since it uses as much as digits as its factorization.
18691 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 432, while the sum is 25.
The square root of 18691 is about 136.7150320923.
The cubic root of 18691 is about 26.5385696816.
The spelling of 18691 in words is "eighteen thousand, six hundred ninety-one".