21546821509 has 4 divisors (see below), whose sum is σ = 21547154860. Its totient is φ = 21546488160.

The previous prime is 21546821477. The next prime is 21546821519. The reversal of 21546821509 is 90512864512.

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 12612413025 + 8934408484 = 112305^2 + 94522^2 .

It is a cyclic number.

It is not a de Polignac number, because 21546821509 - 2⁵ = 21546821477 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 (21546821519) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 35094 + ... + 210535.

It is an arithmetic number, because the mean of its divisors is an integer number (5386788715).

Almost surely, 2^21546821509 is an apocalyptic number.

It is an amenable number.

21546821509 is a deficient number, since it is larger than the sum of its proper divisors (333351).

21546821509 is an equidigital number, since it uses as much as digits as its factorization.

21546821509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 333350.

The product of its (nonzero) digits is 172800, while the sum is 43.

The spelling of 21546821509 in words is "twenty-one billion, five hundred forty-six million, eight hundred twenty-one thousand, five hundred nine".