21100020021 has 8 divisors (see below), whose sum is σ = 31259288960. Its totient is φ = 14066679996.

The previous prime is 21100020001. The next prime is 21100020023. The reversal of 21100020021 is 12002000112.

It is not a de Polignac number, because 21100020021 - 2¹¹ = 21100017973 is a prime.

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

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21100019985 and 21100020012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21100020023) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 390741085 + ... + 390741138.

It is an arithmetic number, because the mean of its divisors is an integer number (3907411120).

Almost surely, 2^21100020021 is an apocalyptic number.

It is an amenable number.

21100020021 is a deficient number, since it is larger than the sum of its proper divisors (10159268939).

21100020021 is an equidigital number, since it uses as much as digits as its factorization.

21100020021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 781482232 (or 781482226 counting only the distinct ones).

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

Adding to 21100020021 its reverse (12002000112), we get a palindrome (33102020133).

The spelling of 21100020021 in words is "twenty-one billion, one hundred million, twenty thousand, twenty-one".