21000100020 has 96 divisors (see below), whose sum is σ = 61511788800. Its totient is φ = 5346130944.

The previous prime is 21000100003. The next prime is 21000100031. The reversal of 21000100020 is 2000100012.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (6).

It is a super Niven number, because it is divisible the sum of any subset of its (nonzero) digits.

It is a junction number, because it is equal to n+sod(n) for n = 21000099981 and 21000100008.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 87057 + ... + 222663.

It is an arithmetic number, because the mean of its divisors is an integer number (640747800).

Almost surely, 2^21000100020 is an apocalyptic number.

21000100020 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 21000100020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30755894400).

21000100020 is an abundant number, since it is smaller than the sum of its proper divisors (40511688780).

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

21000100020 is a wasteful number, since it uses less digits than its factorization.

21000100020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 135737 (or 135735 counting only the distinct ones).

The product of its (nonzero) digits is 4, while the sum is 6.

Adding to 21000100020 its reverse (2000100012), we get a palindrome (23000200032).

The spelling of 21000100020 in words is "twenty-one billion, one hundred thousand, twenty".