17681 has 2 divisors, whose sum is σ = 17682.
Its totient is φ = 17680.
The previous prime is 17669. The next prime is 17683. The reversal of 17681 is 18671.
Subtracting 17681 from its reverse (18671), we obtain a triangular number (990 = T44).
It is a strong prime.
It can be written as a sum of positive squares in only one way, i.e., 13456 + 4225 = 116^2 + 65^2
It is an emirp because it is prime and its reverse (18671) is a distict prime.
It is a cyclic number.
It is not a de Polignac number, because 17681 - 210 = 16657 is a prime.
It is a super-2 number, since 2×176812 = 625235522, which contains 22 as substring.
It is a Sophie Germain prime.
Together with 17683, it forms a pair of twin primes.
It is a Chen prime.
It is a Curzon number.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 17681.
It is not a weakly prime, because it can be changed into another prime (17683) 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, 8840 + 8841.
It is an arithmetic number, because the mean of its divisors is an integer number (8841).
217681 is an apocalyptic number.
It is an amenable number.
17681 is a deficient number, since it is larger than the sum of its proper divisors (1).
17681 is an equidigital number, since it uses as much as digits as its factorization.
17681 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 336, while the sum is 23.
The square root of 17681 is about 132.9699214108.
The cubic root of 17681 is about 26.0516723862.
The spelling of 17681 in words is "seventeen thousand, six hundred eighty-one".