9781 has 2 divisors, whose sum is σ = 9782.
Its totient is φ = 9780.
The previous prime is 9769. The next prime is 9787. The reversal of 9781 is 1879.
9781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.
It is a strong prime.
It can be written as a sum of positive squares in only one way, i.e., 8100 + 1681 = 90^2 + 41^2
It is an emirp because it is prime and its reverse (1879) is a distict prime.
It is a cyclic number.
It is not a de Polignac number, because 9781 - 25 = 9749 is a prime.
It is a super-2 number, since 2×97812 = 191335922, which contains 22 as substring.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (9787) 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, 4890 + 4891.
It is an arithmetic number, because the mean of its divisors is an integer number (4891).
29781 is an apocalyptic number.
It is an amenable number.
9781 is a deficient number, since it is larger than the sum of its proper divisors (1).
9781 is an equidigital number, since it uses as much as digits as its factorization.
9781 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 504, while the sum is 25.
The square root of 9781 is about 98.8989383158.
The cubic root of 9781 is about 21.3859108939.
The spelling of 9781 in words is "nine thousand, seven hundred eighty-one".