21020012109 has 8 divisors (see below), whose sum is σ = 31140758720. Its totient is φ = 14013341388.

The previous prime is 21020012099. The next prime is 21020012129. The reversal of 21020012109 is 90121002012.

It is not a de Polignac number, because 21020012109 - 2¹² = 21020008013 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21020012091 and 21020012100.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21020012129) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 389259457 + ... + 389259510.

It is an arithmetic number, because the mean of its divisors is an integer number (3892594840).

Almost surely, 2^21020012109 is an apocalyptic number.

It is an amenable number.

21020012109 is a deficient number, since it is larger than the sum of its proper divisors (10120746611).

21020012109 is an equidigital number, since it uses as much as digits as its factorization.

21020012109 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 778518976 (or 778518970 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 18.

The spelling of 21020012109 in words is "twenty-one billion, twenty million, twelve thousand, one hundred nine".