21123054805 has 4 divisors (see below), whose sum is σ = 25347665772. Its totient is φ = 16898443840.

The previous prime is 21123054781. The next prime is 21123054817. The reversal of 21123054805 is 50845032112.

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

It can be written as a sum of positive squares in 2 ways, for example, as 11821995441 + 9301059364 = 108729^2 + 96442^2 .

It is not a de Polignac number, because 21123054805 - 2¹⁷ = 21122923733 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2112305476 + ... + 2112305485.

It is an arithmetic number, because the mean of its divisors is an integer number (6336916443).

Almost surely, 2^21123054805 is an apocalyptic number.

It is an amenable number.

21123054805 is a deficient number, since it is larger than the sum of its proper divisors (4224610967).

21123054805 is an equidigital number, since it uses as much as digits as its factorization.

21123054805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4224610966.

The product of its (nonzero) digits is 9600, while the sum is 31.

Adding to 21123054805 its reverse (50845032112), we get a palindrome (71968086917).

The spelling of 21123054805 in words is "twenty-one billion, one hundred twenty-three million, fifty-four thousand, eight hundred five".