21281563 has 4 divisors (see below), whose sum is σ = 22015440. Its totient is φ = 20547688.

The previous prime is 21281543. The next prime is 21281581. The reversal of 21281563 is 36518212.

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

It is a cyclic number.

It is not a de Polignac number, because 21281563 - 2¹⁷ = 21150491 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21281503) 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, 366895 + ... + 366952.

It is an arithmetic number, because the mean of its divisors is an integer number (5503860).

Almost surely, 2^21281563 is an apocalyptic number.

21281563 is a deficient number, since it is larger than the sum of its proper divisors (733877).

21281563 is an equidigital number, since it uses as much as digits as its factorization.

21281563 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 733876.

The product of its digits is 2880, while the sum is 28.

The square root of 21281563 is about 4613.1944463679. The cubic root of 21281563 is about 277.1199808664.

Adding to 21281563 its reverse (36518212), we get a palindrome (57799775).

It can be divided in two parts, 212815 and 63, that added together give a triangular number (212878 = T₆₅₂).

The spelling of 21281563 in words is "twenty-one million, two hundred eighty-one thousand, five hundred sixty-three".