21012100009 has 4 divisors (see below), whose sum is σ = 21058078804. Its totient is φ = 20966121216.

The previous prime is 21012099989. The next prime is 21012100033. The reversal of 21012100009 is 90000121012.

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 19034341225 + 1977758784 = 137965^2 + 44472^2 .

It is a cyclic number.

It is not a de Polignac number, because 21012100009 - 2¹¹ = 21012097961 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21012099965 and 21012100001.

It is not an unprimeable number, because it can be changed into a prime (21012100099) 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, 22988712 + ... + 22989625.

It is an arithmetic number, because the mean of its divisors is an integer number (5264519701).

Almost surely, 2^21012100009 is an apocalyptic number.

It is an amenable number.

21012100009 is a deficient number, since it is larger than the sum of its proper divisors (45978795).

21012100009 is an equidigital number, since it uses as much as digits as its factorization.

21012100009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 45978794.

The product of its (nonzero) digits is 36, while the sum is 16.

The spelling of 21012100009 in words is "twenty-one billion, twelve million, one hundred thousand, nine".