21561040103 has 4 divisors (see below), whose sum is σ = 21566841360. Its totient is φ = 21555238848.

The previous prime is 21561040073. The next prime is 21561040129. The reversal of 21561040103 is 30104016512.

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 21561040103 - 2⁸ = 21561039847 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21561040603) by changing a digit.

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, 2895050 + ... + 2902487.

It is an arithmetic number, because the mean of its divisors is an integer number (5391710340).

Almost surely, 2^21561040103 is an apocalyptic number.

21561040103 is a deficient number, since it is larger than the sum of its proper divisors (5801257).

21561040103 is an equidigital number, since it uses as much as digits as its factorization.

21561040103 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5801256.

The product of its (nonzero) digits is 720, while the sum is 23.

Adding to 21561040103 its reverse (30104016512), we get a palindrome (51665056615).

The spelling of 21561040103 in words is "twenty-one billion, five hundred sixty-one million, forty thousand, one hundred three".