21016420021 has 2 divisors, whose sum is σ = 21016420022. Its totient is φ = 21016420020.

The previous prime is 21016419953. The next prime is 21016420027. The reversal of 21016420021 is 12002461012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20544922225 + 471497796 = 143335^2 + 21714^2 .

It is a cyclic number.

It is not a de Polignac number, because 21016420021 - 2¹⁵ = 21016387253 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21016420027) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10508210010 + 10508210011.

It is an arithmetic number, because the mean of its divisors is an integer number (10508210011).

Almost surely, 2^21016420021 is an apocalyptic number.

It is an amenable number.

21016420021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21016420021 is an equidigital number, since it uses as much as digits as its factorization.

21016420021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 192, while the sum is 19.

Adding to 21016420021 its reverse (12002461012), we get a palindrome (33018881033).

The spelling of 21016420021 in words is "twenty-one billion, sixteen million, four hundred twenty thousand, twenty-one".