9721 has 2 divisors, whose sum is σ = 9722.
Its totient is φ = 9720.
The previous prime is 9719. The next prime is 9733. The reversal of 9721 is 1279.
9721 = T79 + T80 +
It is a weak prime.
It can be written as a sum of positive squares in only one way, i.e., 5625 + 4096 = 75^2 + 64^2
It is an emirp because it is prime and its reverse (1279) is a distict prime.
It is a cyclic number.
It is not a de Polignac number, because 9721 - 21 = 9719 is a prime.
Together with 9719, it forms a pair of twin primes.
It is an Ulam number.
It is a plaindrome in base 13.
It is a nialpdrome in base 10.
It is not a weakly prime, because it can be changed into another prime (9781) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4860 + 4861.
It is an arithmetic number, because the mean of its divisors is an integer number (4861).
29721 is an apocalyptic number.
9721 is the 81-st centered triangular number.
It is an amenable number.
9721 is a deficient number, since it is larger than the sum of its proper divisors (1).
9721 is an equidigital number, since it uses as much as digits as its factorization.
9721 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 126, while the sum is 19.
The square root of 9721 is about 98.5951317257.
The cubic root of 9721 is about 21.3420916729.
The spelling of 9721 in words is "nine thousand, seven hundred twenty-one".