21315243 has 4 divisors (see below), whose sum is σ = 28420328. Its totient is φ = 14210160.

The previous prime is 21315241. The next prime is 21315247. The reversal of 21315243 is 34251312.

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

It is not a de Polignac number, because 21315243 - 2¹ = 21315241 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21315241) 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, 3552538 + ... + 3552543.

It is an arithmetic number, because the mean of its divisors is an integer number (7105082).

Almost surely, 2^21315243 is an apocalyptic number.

21315243 is a deficient number, since it is larger than the sum of its proper divisors (7105085).

21315243 is an equidigital number, since it uses as much as digits as its factorization.

21315243 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7105084.

The product of its digits is 720, while the sum is 21.

The square root of 21315243 is about 4616.8434021526. The cubic root of 21315243 is about 277.2660929671.

Adding to 21315243 its reverse (34251312), we get a palindrome (55566555).

The spelling of 21315243 in words is "twenty-one million, three hundred fifteen thousand, two hundred forty-three".