20019993821 has 2 divisors, whose sum is σ = 20019993822. Its totient is φ = 20019993820.

The previous prime is 20019993809. The next prime is 20019993841. The reversal of 20019993821 is 12839991002.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19079896900 + 940096921 = 138130^2 + 30661^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20019993821 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20019993841) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10009996910 + 10009996911.

It is an arithmetic number, because the mean of its divisors is an integer number (10009996911).

Almost surely, 2^20019993821 is an apocalyptic number.

It is an amenable number.

20019993821 is a deficient number, since it is larger than the sum of its proper divisors (1).

20019993821 is an equidigital number, since it uses as much as digits as its factorization.

20019993821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 69984, while the sum is 44.

The spelling of 20019993821 in words is "twenty billion, nineteen million, nine hundred ninety-three thousand, eight hundred twenty-one".