17721 has 12 divisors (see below), whose sum is σ = 28080. Its totient is φ = 10680.

The previous prime is 17713. The next prime is 17729. The reversal of 17721 is 12771.

It is an interprime number because it is at equal distance from previous prime (17713) and next prime (17729).

It is not a de Polignac number, because 17721 - 2³ = 17713 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 17694 and 17703.

It is not an unprimeable number, because it can be changed into a prime (17729) 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 in 11 ways as a sum of consecutive naturals, for example, 10 + ... + 188.

It is an arithmetic number, because the mean of its divisors is an integer number (2340).

2¹⁷⁷²¹ is an apocalyptic number.

17721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

17721 is a deficient number, since it is larger than the sum of its proper divisors (10359).

17721 is a wasteful number, since it uses less digits than its factorization.

17721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 196 (or 193 counting only the distinct ones).

The product of its digits is 98, while the sum is 18.

The square root of 17721 is about 133.1202463940. The cubic root of 17721 is about 26.0713032905.

Subtracting from 17721 its reverse (12771), we obtain a triangular number (4950 = T₉₉).

The spelling of 17721 in words is "seventeen thousand, seven hundred twenty-one", and thus it is an iban number.