21204210221 has 2 divisors, whose sum is σ = 21204210222. Its totient is φ = 21204210220.

The previous prime is 21204210199. The next prime is 21204210239. The reversal of 21204210221 is 12201240212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20906268100 + 297942121 = 144590^2 + 17261^2 .

It is a cyclic number.

It is not a de Polignac number, because 21204210221 - 2²⁶ = 21137101357 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21204210221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21204210241) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10602105110 + 10602105111.

It is an arithmetic number, because the mean of its divisors is an integer number (10602105111).

Almost surely, 2^21204210221 is an apocalyptic number.

It is an amenable number.

21204210221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21204210221 is an equidigital number, since it uses as much as digits as its factorization.

21204210221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 128, while the sum is 17.

Adding to 21204210221 its reverse (12201240212), we get a palindrome (33405450433).

The spelling of 21204210221 in words is "twenty-one billion, two hundred four million, two hundred ten thousand, two hundred twenty-one".