21109243 has 2 divisors, whose sum is σ = 21109244. Its totient is φ = 21109242.

The previous prime is 21109241. The next prime is 21109261. The reversal of 21109243 is 34290112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21109243 - 2¹ = 21109241 is a prime.

Together with 21109241, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21109241) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10554621 + 10554622.

It is an arithmetic number, because the mean of its divisors is an integer number (10554622).

Almost surely, 2^21109243 is an apocalyptic number.

21109243 is a deficient number, since it is larger than the sum of its proper divisors (1).

21109243 is an equidigital number, since it uses as much as digits as its factorization.

21109243 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 432, while the sum is 22.

The square root of 21109243 is about 4594.4796223294. The cubic root of 21109243 is about 276.3699923023.

Adding to 21109243 its reverse (34290112), we get a palindrome (55399355).

The spelling of 21109243 in words is "twenty-one million, one hundred nine thousand, two hundred forty-three".