243809921 has 4 divisors (see below), whose sum is σ = 244022532. Its totient is φ = 243597312.

The previous prime is 243809899. The next prime is 243809939. The reversal of 243809921 is 129908342.

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 95335696 + 148474225 = 9764^2 + 12185^2 .

It is a cyclic number.

It is not a de Polignac number, because 243809921 - 2⁶ = 243809857 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (243809981) 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, 104576 + ... + 106881.

It is an arithmetic number, because the mean of its divisors is an integer number (61005633).

Almost surely, 2^243809921 is an apocalyptic number.

It is an amenable number.

243809921 is a deficient number, since it is larger than the sum of its proper divisors (212611).

243809921 is a wasteful number, since it uses less digits than its factorization.

243809921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 212610.

The product of its (nonzero) digits is 31104, while the sum is 38.

The square root of 243809921 is about 15614.4138858940. The cubic root of 243809921 is about 624.7176717377.

The spelling of 243809921 in words is "two hundred forty-three million, eight hundred nine thousand, nine hundred twenty-one".