243881821 has 4 divisors (see below), whose sum is σ = 244047100. Its totient is φ = 243716544.

The previous prime is 243881801. The next prime is 243881839. The reversal of 243881821 is 128188342.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 128188342 = 2 ⋅64094171.

It can be written as a sum of positive squares in 2 ways, for example, as 40819321 + 203062500 = 6389^2 + 14250^2 .

It is a cyclic number.

It is not a de Polignac number, because 243881821 - 2⁵ = 243881789 is a prime.

It is a super-2 number, since 2×243881821² = 118956685228552082, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (243881801) 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, 80406 + ... + 83383.

It is an arithmetic number, because the mean of its divisors is an integer number (61011775).

Almost surely, 2^243881821 is an apocalyptic number.

It is an amenable number.

243881821 is a deficient number, since it is larger than the sum of its proper divisors (165279).

243881821 is a wasteful number, since it uses less digits than its factorization.

243881821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 165278.

The product of its digits is 24576, while the sum is 37.

The square root of 243881821 is about 15616.7160760513. The cubic root of 243881821 is about 624.7790758372.

The spelling of 243881821 in words is "two hundred forty-three million, eight hundred eighty-one thousand, eight hundred twenty-one".