21115351021 has 2 divisors, whose sum is σ = 21115351022. Its totient is φ = 21115351020.

The previous prime is 21115351013. The next prime is 21115351057. The reversal of 21115351021 is 12015351112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10653129796 + 10462221225 = 103214^2 + 102285^2 .

It is a cyclic number.

It is not a de Polignac number, because 21115351021 - 2³ = 21115351013 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21115350983 and 21115351001.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21115351091) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10557675510 + 10557675511.

It is an arithmetic number, because the mean of its divisors is an integer number (10557675511).

Almost surely, 2^21115351021 is an apocalyptic number.

It is an amenable number.

21115351021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21115351021 is an equidigital number, since it uses as much as digits as its factorization.

21115351021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 300, while the sum is 22.

Subtracting from 21115351021 its reverse (12015351112), we obtain a palindrome (9099999909).

The spelling of 21115351021 in words is "twenty-one billion, one hundred fifteen million, three hundred fifty-one thousand, twenty-one".