21000000000 has 400 divisors, whose sum is σ = 79921866816. Its totient is φ = 4800000000.

The previous prime is 20999999981. The next prime is 21000000019. The reversal of 21000000000 is 12.

It is an interprime number because it is at equal distance from previous prime (20999999981) and next prime (21000000019).

It is a tau number, because it is divible by the number of its divisors (400).

It is a Harshad number since it is a multiple of its sum of digits (3).

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

It is a nialpdrome in base 10.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 2999999997 + ... + 3000000003.

Almost surely, 2^21000000000 is an apocalyptic number.

21000000000 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 21000000000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39960933408).

21000000000 is an abundant number, since it is smaller than the sum of its proper divisors (58921866816).

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

21000000000 is an frugal number, since it uses more digits than its factorization.

21000000000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 73 (or 17 counting only the distinct ones).

The product of its (nonzero) digits is 2, while the sum is 3.

Adding to 21000000000 its reverse (12), we get a palindrome (21000000012).

The spelling of 21000000000 in words is "twenty-one billion", and thus it is an aban number and an uban number.