21000002120 has 64 divisors (see below), whose sum is σ = 47832735600. Its totient is φ = 8296611840.

The previous prime is 21000002083. The next prime is 21000002129. The reversal of 21000002120 is 2120000012.

It can be written as a sum of positive squares in 8 ways, for example, as 63648484 + 20936353636 = 7978^2 + 144694^2 .

It is a Harshad number since it is a multiple of its sum of digits (8).

It is a junction number, because it is equal to n+sod(n) for n = 21000002098 and 21000002107.

It is not an unprimeable number, because it can be changed into a prime (21000002129) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3973880 + ... + 3979160.

Almost surely, 2^21000002120 is an apocalyptic number.

21000002120 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21000002120, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23916367800).

21000002120 is an abundant number, since it is smaller than the sum of its proper divisors (26832733480).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21000002120 is a wasteful number, since it uses less digits than its factorization.

21000002120 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6498 (or 6494 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 8.

Adding to 21000002120 its reverse (2120000012), we get a palindrome (23120002132).

The spelling of 21000002120 in words is "twenty-one billion, two thousand, one hundred twenty".