19721120021 has 2 divisors, whose sum is σ = 19721120022. Its totient is φ = 19721120020.

The previous prime is 19721119981. The next prime is 19721120033. The reversal of 19721120021 is 12002112791.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18896626225 + 824493796 = 137465^2 + 28714^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19721120021 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19721120071) 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, 9860560010 + 9860560011.

It is an arithmetic number, because the mean of its divisors is an integer number (9860560011).

Almost surely, 2^19721120021 is an apocalyptic number.

It is an amenable number.

19721120021 is a deficient number, since it is larger than the sum of its proper divisors (1).

19721120021 is an equidigital number, since it uses as much as digits as its factorization.

19721120021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 504, while the sum is 26.

The spelling of 19721120021 in words is "nineteen billion, seven hundred twenty-one million, one hundred twenty thousand, twenty-one".