21100012020 has 72 divisors (see below), whose sum is σ = 64328368104. Its totient is φ = 5598098688.

The previous prime is 21100012013. The next prime is 21100012039. The reversal of 21100012020 is 2021000112.

It can be written as a sum of positive squares in 4 ways, for example, as 13307006736 + 7793005284 = 115356^2 + 88278^2 .

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 = 21100011993 and 21100012011.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 262059 + ... + 332978.

It is an arithmetic number, because the mean of its divisors is an integer number (893449557).

Almost surely, 2^21100012020 is an apocalyptic number.

21100012020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21100012020 is an abundant number, since it is smaller than the sum of its proper divisors (43228356084).

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

21100012020 is a wasteful number, since it uses less digits than its factorization.

21100012020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 595249 (or 595244 counting only the distinct ones).

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

Adding to 21100012020 its reverse (2021000112), we get a palindrome (23121012132).

The spelling of 21100012020 in words is "twenty-one billion, one hundred million, twelve thousand, twenty".