201721 has 8 divisors (see below), whose sum is σ = 221760. Its totient is φ = 182352.

The previous prime is 201709. The next prime is 201731. The reversal of 201721 is 127102.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 201721 - 2⁹ = 201209 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (13).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (201701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 636 + ... + 898.

It is an arithmetic number, because the mean of its divisors is an integer number (27720).

2²⁰¹⁷²¹ is an apocalyptic number.

It is an amenable number.

201721 is a deficient number, since it is larger than the sum of its proper divisors (20039).

201721 is a wasteful number, since it uses less digits than its factorization.

201721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 335.

The product of its (nonzero) digits is 28, while the sum is 13.

The square root of 201721 is about 449.1336104101. The cubic root of 201721 is about 58.6476170646.

Adding to 201721 its reverse (127102), we get a palindrome (328823).

The spelling of 201721 in words is "two hundred one thousand, seven hundred twenty-one", and thus it is an iban number.