21278563 has 4 divisors (see below), whose sum is σ = 21308560. Its totient is φ = 21248568.

The previous prime is 21278557. The next prime is 21278567. The reversal of 21278563 is 36587212.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21278563 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21278567) 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, 13908 + ... + 15361.

It is an arithmetic number, because the mean of its divisors is an integer number (5327140).

Almost surely, 2^21278563 is an apocalyptic number.

21278563 is a deficient number, since it is larger than the sum of its proper divisors (29997).

21278563 is an equidigital number, since it uses as much as digits as its factorization.

21278563 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29996.

The product of its digits is 20160, while the sum is 34.

The square root of 21278563 is about 4612.8692806105. The cubic root of 21278563 is about 277.1069586554.

The spelling of 21278563 in words is "twenty-one million, two hundred seventy-eight thousand, five hundred sixty-three".