1721 has 2 divisors, whose sum is σ = 1722.
Its totient is φ = 1720.
The previous prime is 1709. The next prime is 1723. The reversal of 1721 is 1271.
It is a strong prime.
It can be written as a sum of positive squares in only one way, i.e., 1600 + 121 = 40^2 + 11^2
It is a cyclic number.
It is not a de Polignac number, because 1721 - 26 = 1657 is a prime.
Together with 1723, it forms a pair of twin primes.
It is a Chen prime.
It is an Ulam number.
It is a plaindrome in base 14 and base 15.
It is a nialpdrome in base 12.
It is not a weakly prime, because it can be changed into another prime (1723) 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, 860 + 861.
It is an arithmetic number, because the mean of its divisors is an integer number (861).
It is an amenable number.
1721 is a deficient number, since it is larger than the sum of its proper divisors (1).
1721 is an equidigital number, since it uses as much as digits as its factorization.
1721 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 14, while the sum is 11.
The square root of 1721 is about 41.4849370254.
The cubic root of 1721 is about 11.9837743669.
Adding to 1721 its reverse (1271), we get a palindrome (2992).
The spelling of 1721 in words is "one thousand, seven hundred twenty-one", and thus it is an iban number.