243221821 has 2 divisors, whose sum is σ = 243221822. Its totient is φ = 243221820.

The previous prime is 243221819. The next prime is 243221833. The reversal of 243221821 is 128122342.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 140422500 + 102799321 = 11850^2 + 10139^2 .

It is a cyclic number.

It is not a de Polignac number, because 243221821 - 2¹ = 243221819 is a prime.

Together with 243221819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (243221921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 121610910 + 121610911.

It is an arithmetic number, because the mean of its divisors is an integer number (121610911).

Almost surely, 2^243221821 is an apocalyptic number.

It is an amenable number.

243221821 is a deficient number, since it is larger than the sum of its proper divisors (1).

243221821 is an equidigital number, since it uses as much as digits as its factorization.

243221821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1536, while the sum is 25.

The square root of 243221821 is about 15595.5705570524. The cubic root of 243221821 is about 624.2149682932.

The spelling of 243221821 in words is "two hundred forty-three million, two hundred twenty-one thousand, eight hundred twenty-one".