21117121021 has 2 divisors, whose sum is σ = 21117121022. Its totient is φ = 21117121020.

The previous prime is 21117120989. The next prime is 21117121033. The reversal of 21117121021 is 12012171112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17007028921 + 4110092100 = 130411^2 + 64110^2 .

It is a cyclic number.

It is not a de Polignac number, because 21117121021 - 2⁵ = 21117120989 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21117121021.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21117127021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10558560510 + 10558560511.

It is an arithmetic number, because the mean of its divisors is an integer number (10558560511).

Almost surely, 2^21117121021 is an apocalyptic number.

It is an amenable number.

21117121021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21117121021 is an equidigital number, since it uses as much as digits as its factorization.

21117121021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 56, while the sum is 19.

Adding to 21117121021 its reverse (12012171112), we get a palindrome (33129292133).

The spelling of 21117121021 in words is "twenty-one billion, one hundred seventeen million, one hundred twenty-one thousand, twenty-one".