21100021020 has 96 divisors (see below), whose sum is σ = 70694111040. Its totient is φ = 5193849600.

The previous prime is 21100021001. The next prime is 21100021021. The reversal of 21100021020 is 2012000112.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a junction number, because it is equal to n+sod(n) for n = 21100020993 and 21100021011.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21100021021) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1495831 + ... + 1509870.

It is an arithmetic number, because the mean of its divisors is an integer number (736396990).

Almost surely, 2^21100021020 is an apocalyptic number.

21100021020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21100021020 is an abundant number, since it is smaller than the sum of its proper divisors (49594090020).

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

21100021020 is a wasteful number, since it uses less digits than its factorization.

21100021020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3005732 (or 3005724 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 9.

Adding to 21100021020 its reverse (2012000112), we get a palindrome (23112021132).

The spelling of 21100021020 in words is "twenty-one billion, one hundred million, twenty-one thousand, twenty".