21000021000 has 256 divisors, whose sum is σ = 75629099520. Its totient is φ = 4752000000.

The previous prime is 21000020999. The next prime is 21000021019. The reversal of 21000021000 is 12000012.

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 self number, because there is not a number n which added to its sum of digits gives 21000021000.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 2116050 + ... + 2125950.

It is an arithmetic number, because the mean of its divisors is an integer number (295426170).

Almost surely, 2^21000021000 is an apocalyptic number.

21000021000 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 21000021000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37814549760).

21000021000 is an abundant number, since it is smaller than the sum of its proper divisors (54629078520).

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

21000021000 is a wasteful number, since it uses less digits than its factorization.

21000021000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10033 (or 10019 counting only the distinct ones).

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

Adding to 21000021000 its reverse (12000012), we get a palindrome (21012021012).

The spelling of 21000021000 in words is "twenty-one billion, twenty-one thousand".