21216247 has 4 divisors (see below), whose sum is σ = 22848280. Its totient is φ = 19584216.

The previous prime is 21216241. The next prime is 21216253. The reversal of 21216247 is 74261212.

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

It is an interprime number because it is at equal distance from previous prime (21216241) and next prime (21216253).

It is a cyclic number.

It is not a de Polignac number, because 21216247 - 2¹⁹ = 20691959 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21216241) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 815997 + ... + 816022.

It is an arithmetic number, because the mean of its divisors is an integer number (5712070).

Almost surely, 2^21216247 is an apocalyptic number.

21216247 is a deficient number, since it is larger than the sum of its proper divisors (1632033).

21216247 is a wasteful number, since it uses less digits than its factorization.

21216247 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1632032.

The product of its digits is 1344, while the sum is 25.

The square root of 21216247 is about 4606.1097468471. The cubic root of 21216247 is about 276.8361840763.

Adding to 21216247 its reverse (74261212), we get a palindrome (95477459).

The spelling of 21216247 in words is "twenty-one million, two hundred sixteen thousand, two hundred forty-seven".