21320309921 has 2 divisors, whose sum is σ = 21320309922. Its totient is φ = 21320309920.

The previous prime is 21320309893. The next prime is 21320309981. The reversal of 21320309921 is 12990302312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19227704896 + 2092605025 = 138664^2 + 45745^2 .

It is a cyclic number.

It is not a de Polignac number, because 21320309921 - 2¹⁰ = 21320308897 is a prime.

It is not a weakly prime, because it can be changed into another prime (21320309981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10660154960 + 10660154961.

It is an arithmetic number, because the mean of its divisors is an integer number (10660154961).

Almost surely, 2^21320309921 is an apocalyptic number.

It is an amenable number.

21320309921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21320309921 is an equidigital number, since it uses as much as digits as its factorization.

21320309921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5832, while the sum is 32.

The spelling of 21320309921 in words is "twenty-one billion, three hundred twenty million, three hundred nine thousand, nine hundred twenty-one".