21813442561 has 4 divisors (see below), whose sum is σ = 21813858900. Its totient is φ = 21813026224.

The previous prime is 21813442549. The next prime is 21813442571. The reversal of 21813442561 is 16524431812.

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 14669812161 + 7143630400 = 121119^2 + 84520^2 .

It is a cyclic number.

It is not a de Polignac number, because 21813442561 - 2⁵ = 21813442529 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21813442561.

It is not an unprimeable number, because it can be changed into a prime (21813442501) 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, 115966 + ... + 238903.

It is an arithmetic number, because the mean of its divisors is an integer number (5453464725).

Almost surely, 2^21813442561 is an apocalyptic number.

It is an amenable number.

21813442561 is a deficient number, since it is larger than the sum of its proper divisors (416339).

21813442561 is an equidigital number, since it uses as much as digits as its factorization.

21813442561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 416338.

The product of its digits is 46080, while the sum is 37.

The spelling of 21813442561 in words is "twenty-one billion, eight hundred thirteen million, four hundred forty-two thousand, five hundred sixty-one".