21111101212121 has 2 divisors, whose sum is σ = 21111101212122. Its totient is φ = 21111101212120.

The previous prime is 21111101212099. The next prime is 21111101212127. The reversal of 21111101212121 is 12121210111112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11486432618896 + 9624668593225 = 3389164^2 + 3102365^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21111101212121 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21111101212121.

It is not a weakly prime, because it can be changed into another prime (21111101212127) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10555550606060 + 10555550606061.

It is an arithmetic number, because the mean of its divisors is an integer number (10555550606061).

Almost surely, 2^{21111101212121} is an apocalyptic number.

It is an amenable number.

21111101212121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21111101212121 is an equidigital number, since it uses as much as digits as its factorization.

21111101212121 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 16, while the sum is 17.

Adding to 21111101212121 its reverse (12121210111112), we get a palindrome (33232311323233).

The spelling of 21111101212121 in words is "twenty-one trillion, one hundred eleven billion, one hundred one million, two hundred twelve thousand, one hundred twenty-one".