243821 has 4 divisors (see below), whose sum is σ = 245532. Its totient is φ = 242112.

The previous prime is 243809. The next prime is 243829. The reversal of 243821 is 128342.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 128342 = 2 ⋅64171.

It can be written as a sum of positive squares in 2 ways, for example, as 45796 + 198025 = 214^2 + 445^2 .

It is a cyclic number.

It is not a de Polignac number, because 243821 - 2¹⁰ = 242797 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 243793 and 243802.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 243821.

It is not an unprimeable number, because it can be changed into a prime (243829) 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 3 ways as a sum of consecutive naturals, for example, 620 + ... + 933.

It is an arithmetic number, because the mean of its divisors is an integer number (61383).

2²⁴³⁸²¹ is an apocalyptic number.

It is an amenable number.

243821 is a deficient number, since it is larger than the sum of its proper divisors (1711).

243821 is a wasteful number, since it uses less digits than its factorization.

243821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1710.

The product of its digits is 384, while the sum is 20.

The square root of 243821 is about 493.7823407130. The cubic root of 243821 is about 62.4727134221.

The spelling of 243821 in words is "two hundred forty-three thousand, eight hundred twenty-one".