21105563 has 2 divisors, whose sum is σ = 21105564. Its totient is φ = 21105562.

The previous prime is 21105547. The next prime is 21105569. The reversal of 21105563 is 36550112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21105563 - 2⁴ = 21105547 is a prime.

It is not a weakly prime, because it can be changed into another prime (21105569) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10552781 + 10552782.

It is an arithmetic number, because the mean of its divisors is an integer number (10552782).

Almost surely, 2^21105563 is an apocalyptic number.

21105563 is a deficient number, since it is larger than the sum of its proper divisors (1).

21105563 is an equidigital number, since it uses as much as digits as its factorization.

21105563 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 900, while the sum is 23.

The square root of 21105563 is about 4594.0791242642. The cubic root of 21105563 is about 276.3539313967.

Adding to 21105563 its reverse (36550112), we get a palindrome (57655675).

The spelling of 21105563 in words is "twenty-one million, one hundred five thousand, five hundred sixty-three".