21215243 has 4 divisors (see below), whose sum is σ = 24246000. Its totient is φ = 18184488.

The previous prime is 21215237. The next prime is 21215261. The reversal of 21215243 is 34251212.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21215243 - 2²⁰ = 20166667 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21215203) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1515368 + ... + 1515381.

It is an arithmetic number, because the mean of its divisors is an integer number (6061500).

Almost surely, 2^21215243 is an apocalyptic number.

21215243 is a deficient number, since it is larger than the sum of its proper divisors (3030757).

21215243 is an equidigital number, since it uses as much as digits as its factorization.

21215243 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3030756.

The product of its digits is 480, while the sum is 20.

The square root of 21215243 is about 4606.0007598784. Note that the first 3 decimals coincide. The cubic root of 21215243 is about 276.8318171727.

Adding to 21215243 its reverse (34251212), we get a palindrome (55466455).

The spelling of 21215243 in words is "twenty-one million, two hundred fifteen thousand, two hundred forty-three".