21212112121 has 2 divisors, whose sum is σ = 21212112122. Its totient is φ = 21212112120.

The previous prime is 21212112113. The next prime is 21212112139. The reversal of 21212112121 is 12121121212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16727800896 + 4484311225 = 129336^2 + 66965^2 .

It is a cyclic number.

It is not a de Polignac number, because 21212112121 - 2³ = 21212112113 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21212112095 and 21212112104.

It is not a weakly prime, because it can be changed into another prime (21212112101) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606056060 + 10606056061.

It is an arithmetic number, because the mean of its divisors is an integer number (10606056061).

Almost surely, 2^21212112121 is an apocalyptic number.

It is an amenable number.

21212112121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21212112121 is an equidigital number, since it uses as much as digits as its factorization.

21212112121 is an evil number, because the sum of its binary digits is even.

The product of its digits is 32, while the sum is 16.

Adding to 21212112121 its reverse (12121121212), we get a palindrome (33333233333).

Subtracting from 21212112121 its reverse (12121121212), we obtain a palindrome (9090990909).

It can be divided in two parts, 2 and 1212112121, that multiplied together give a palindrome (2424224242).

The spelling of 21212112121 in words is "twenty-one billion, two hundred twelve million, one hundred twelve thousand, one hundred twenty-one".