21210212121221 has 2 divisors, whose sum is σ = 21210212121222. Its totient is φ = 21210212121220.

The previous prime is 21210212121211. The next prime is 21210212121233. The reversal of 21210212121221 is 12212121201212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17735772040996 + 3474440080225 = 4211386^2 + 1863985^2 .

It is a cyclic number.

It is not a de Polignac number, because 21210212121221 - 2¹⁸ = 21210211859077 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21210212121193 and 21210212121202.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21210212121211) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605106060610 + 10605106060611.

It is an arithmetic number, because the mean of its divisors is an integer number (10605106060611).

Almost surely, 2^{21210212121221} is an apocalyptic number.

It is an amenable number.

21210212121221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21210212121221 is an equidigital number, since it uses as much as digits as its factorization.

21210212121221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 128, while the sum is 20.

Adding to 21210212121221 its reverse (12212121201212), we get a palindrome (33422333322433).

The spelling of 21210212121221 in words is "twenty-one trillion, two hundred ten billion, two hundred twelve million, one hundred twenty-one thousand, two hundred twenty-one".