211721 has 4 divisors (see below), whose sum is σ = 213012. Its totient is φ = 210432.

The previous prime is 211711. The next prime is 211723. The reversal of 211721 is 127112.

211721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 55696 + 156025 = 236^2 + 395^2 .

It is a cyclic number.

It is not a de Polignac number, because 211721 - 2⁶ = 211657 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 211696 and 211705.

It is not an unprimeable number, because it can be changed into a prime (211723) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 356 + ... + 741.

It is an arithmetic number, because the mean of its divisors is an integer number (53253).

2²¹¹⁷²¹ is an apocalyptic number.

It is an amenable number.

211721 is a deficient number, since it is larger than the sum of its proper divisors (1291).

211721 is a wasteful number, since it uses less digits than its factorization.

211721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1290.

The product of its digits is 28, while the sum is 14.

The square root of 211721 is about 460.1315029424. The cubic root of 211721 is about 59.6011508268.

Adding to 211721 its reverse (127112), we get a palindrome (338833).

The spelling of 211721 in words is "two hundred eleven thousand, seven hundred twenty-one", and thus it is an iban number.