21010100021 has 2 divisors, whose sum is σ = 21010100022. Its totient is φ = 21010100020.

The previous prime is 21010099987. The next prime is 21010100039. The reversal of 21010100021 is 12000101012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12374115121 + 8635984900 = 111239^2 + 92930^2 .

It is a cyclic number.

It is not a de Polignac number, because 21010100021 - 2¹⁰ = 21010098997 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21010099981 and 21010100008.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21010100071) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10505050010 + 10505050011.

It is an arithmetic number, because the mean of its divisors is an integer number (10505050011).

Almost surely, 2^21010100021 is an apocalyptic number.

It is an amenable number.

21010100021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21010100021 is an equidigital number, since it uses as much as digits as its factorization.

21010100021 is an evil number, because the sum of its binary digits is even.

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

Adding to 21010100021 its reverse (12000101012), we get a palindrome (33010201033).

Subtracting from 21010100021 its reverse (12000101012), we obtain a palindrome (9009999009).

The spelling of 21010100021 in words is "twenty-one billion, ten million, one hundred thousand, twenty-one".