21210111100021 has 2 divisors, whose sum is σ = 21210111100022. Its totient is φ = 21210111100020.

The previous prime is 21210111099977. The next prime is 21210111100027. The reversal of 21210111100021 is 12000111101212.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20945395704996 + 264715395025 = 4576614^2 + 514505^2 .

It is a cyclic number.

It is not a de Polignac number, because 21210111100021 - 2¹⁹ = 21210110575733 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21210111099974 and 21210111100010.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21210111100027) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605055550010 + 10605055550011.

It is an arithmetic number, because the mean of its divisors is an integer number (10605055550011).

Almost surely, 2^{21210111100021} is an apocalyptic number.

It is an amenable number.

21210111100021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21210111100021 is an equidigital number, since it uses as much as digits as its factorization.

21210111100021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 8, while the sum is 13.

Adding to 21210111100021 its reverse (12000111101212), we get a palindrome (33210222201233).

The spelling of 21210111100021 in words is "twenty-one trillion, two hundred ten billion, one hundred eleven million, one hundred thousand, twenty-one".