21644247 has 8 divisors (see below), whose sum is σ = 30556656. Its totient is φ = 13580672.

The previous prime is 21644197. The next prime is 21644257. The reversal of 21644247 is 74244612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21644247 - 2¹¹ = 21642199 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21644257) 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 in 7 ways as a sum of consecutive naturals, for example, 212148 + ... + 212249.

It is an arithmetic number, because the mean of its divisors is an integer number (3819582).

Almost surely, 2^21644247 is an apocalyptic number.

21644247 is a deficient number, since it is larger than the sum of its proper divisors (8912409).

21644247 is a wasteful number, since it uses less digits than its factorization.

21644247 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 424417.

The product of its digits is 10752, while the sum is 30.

The square root of 21644247 is about 4652.3377994294. The cubic root of 21644247 is about 278.6853636321.

Adding to 21644247 its reverse (74244612), we get a palindrome (95888859).

The spelling of 21644247 in words is "twenty-one million, six hundred forty-four thousand, two hundred forty-seven".