21200021020 has 144 divisors (see below), whose sum is σ = 50374039968. Its totient is φ = 7466434560.

The previous prime is 21200021009. The next prime is 21200021027. The reversal of 21200021020 is 2012000212.

It is a Harshad number since it is a multiple of its sum of digits (10).

It is a junction number, because it is equal to n+sod(n) for n = 21200020988 and 21200021006.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21200021027) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 10186380 + ... + 10188460.

It is an arithmetic number, because the mean of its divisors is an integer number (349819722).

Almost surely, 2^21200021020 is an apocalyptic number.

21200021020 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 21200021020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25187019984).

21200021020 is an abundant number, since it is smaller than the sum of its proper divisors (29174018948).

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

21200021020 is a wasteful number, since it uses less digits than its factorization.

21200021020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2228 (or 2207 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 10.

Adding to 21200021020 its reverse (2012000212), we get a palindrome (23212021232).

The spelling of 21200021020 in words is "twenty-one billion, two hundred million, twenty-one thousand, twenty".