21001000100021 has 8 divisors (see below), whose sum is σ = 21444076904664. Its totient is φ = 20562123075840.

The previous prime is 21001000099949. The next prime is 21001000100057. The reversal of 21001000100021 is 12000100010012.

It can be written as a sum of positive squares in 4 ways, for example, as 4569440640625 + 16431559459396 = 2137625^2 + 4053586^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21001000100021 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21001000099981 and 21001000100008.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001000100081) 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, 1049935010 + ... + 1049955011.

It is an arithmetic number, because the mean of its divisors is an integer number (2680509613083).

Almost surely, 2^{21001000100021} is an apocalyptic number.

It is an amenable number.

21001000100021 is a deficient number, since it is larger than the sum of its proper divisors (443076804643).

21001000100021 is a wasteful number, since it uses less digits than its factorization.

21001000100021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2099890231.

The product of its (nonzero) digits is 4, while the sum is 8.

Adding to 21001000100021 its reverse (12000100010012), we get a palindrome (33001100110033).

Subtracting from 21001000100021 its reverse (12000100010012), we obtain a palindrome (9000900090009).

The spelling of 21001000100021 in words is "twenty-one trillion, one billion, one hundred thousand, twenty-one".