21245563 has 4 divisors (see below), whose sum is σ = 22495320. Its totient is φ = 19995808.

The previous prime is 21245561. The next prime is 21245617. The reversal of 21245563 is 36554212.

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

It is not a de Polignac number, because 21245563 - 2¹ = 21245561 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21245561) 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 3 ways as a sum of consecutive naturals, for example, 624853 + ... + 624886.

It is an arithmetic number, because the mean of its divisors is an integer number (5623830).

Almost surely, 2^21245563 is an apocalyptic number.

21245563 is a deficient number, since it is larger than the sum of its proper divisors (1249757).

21245563 is a wasteful number, since it uses less digits than its factorization.

21245563 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1249756.

The product of its digits is 7200, while the sum is 28.

The square root of 21245563 is about 4609.2909433014. The cubic root of 21245563 is about 276.9636334851.

Adding to 21245563 its reverse (36554212), we get a palindrome (57799775).

The spelling of 21245563 in words is "twenty-one million, two hundred forty-five thousand, five hundred sixty-three".