18731 has 2 divisors, whose sum is σ = 18732. Its totient is φ = 18730.

The previous prime is 18719. The next prime is 18743. The reversal of 18731 is 13781.

18731 = T₇₆ + T₇₇ + ... + T₈₁.

It is a balanced prime because it is at equal distance from previous prime (18719) and next prime (18743).

It is an emirp because it is prime and its reverse (13781) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18731 - 2¹⁰ = 17707 is a prime.

It is a super-2 number, since 2×18731² = 701700722, which contains 22 as substring.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (18701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9365 + 9366.

It is an arithmetic number, because the mean of its divisors is an integer number (9366).

2¹⁸⁷³¹ is an apocalyptic number.

18731 is a deficient number, since it is larger than the sum of its proper divisors (1).

18731 is an equidigital number, since it uses as much as digits as its factorization.

18731 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 168, while the sum is 20.

The square root of 18731 is about 136.8612436010. The cubic root of 18731 is about 26.5574876355.

Subtracting from 18731 its reverse (13781), we obtain a triangular number (4950 = T₉₉).

The spelling of 18731 in words is "eighteen thousand, seven hundred thirty-one".