243721 has 4 divisors (see below), whose sum is σ = 244944. Its totient is φ = 242500.

The previous prime is 243709. The next prime is 243769. The reversal of 243721 is 127342.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 127342 = 2 ⋅63671.

It is a cyclic number.

It is not a de Polignac number, because 243721 - 2⁹ = 243209 is a prime.

It is a Duffinian number.

243721 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (243701) 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, 235 + ... + 736.

It is an arithmetic number, because the mean of its divisors is an integer number (61236).

2²⁴³⁷²¹ is an apocalyptic number.

It is an amenable number.

243721 is a deficient number, since it is larger than the sum of its proper divisors (1223).

243721 is an equidigital number, since it uses as much as digits as its factorization.

243721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1222.

The product of its digits is 336, while the sum is 19.

The square root of 243721 is about 493.6810711380. The cubic root of 243721 is about 62.4641714650.

The spelling of 243721 in words is "two hundred forty-three thousand, seven hundred twenty-one", and thus it is an iban number.