21123122021 has 2 divisors, whose sum is σ = 21123122022. Its totient is φ = 21123122020.

The previous prime is 21123122011. The next prime is 21123122057. The reversal of 21123122021 is 12022132112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12980044900 + 8143077121 = 113930^2 + 90239^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21123122021 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21123122011) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10561561010 + 10561561011.

It is an arithmetic number, because the mean of its divisors is an integer number (10561561011).

Almost surely, 2^21123122021 is an apocalyptic number.

It is an amenable number.

21123122021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21123122021 is an equidigital number, since it uses as much as digits as its factorization.

21123122021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 96, while the sum is 17.

Adding to 21123122021 its reverse (12022132112), we get a palindrome (33145254133).

The spelling of 21123122021 in words is "twenty-one billion, one hundred twenty-three million, one hundred twenty-two thousand, twenty-one".