21900018505 has 4 divisors (see below), whose sum is σ = 26280022212. Its totient is φ = 17520014800.

The previous prime is 21900018493. The next prime is 21900018523. The reversal of 21900018505 is 50581000912.

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 7205972544 + 14694045961 = 84888^2 + 121219^2 .

It is not a de Polignac number, because 21900018505 - 2⁷ = 21900018377 is a prime.

It is a super-2 number, since 2×21900018505² (a number of 21 digits) contains 22 as substring.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian 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, 2190001846 + ... + 2190001855.

It is an arithmetic number, because the mean of its divisors is an integer number (6570005553).

Almost surely, 2^21900018505 is an apocalyptic number.

It is an amenable number.

21900018505 is a deficient number, since it is larger than the sum of its proper divisors (4380003707).

21900018505 is an equidigital number, since it uses as much as digits as its factorization.

21900018505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4380003706.

The product of its (nonzero) digits is 3600, while the sum is 31.

The spelling of 21900018505 in words is "twenty-one billion, nine hundred million, eighteen thousand, five hundred five".