19819859821 has 2 divisors, whose sum is σ = 19819859822. Its totient is φ = 19819859820.

The previous prime is 19819859803. The next prime is 19819859831. The reversal of 19819859821 is 12895891891.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19789455625 + 30404196 = 140675^2 + 5514^2 .

It is an emirp because it is prime and its reverse (12895891891) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19819859821 - 2¹⁹ = 19819335533 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 19819859821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19819859831) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9909929910 + 9909929911.

It is an arithmetic number, because the mean of its divisors is an integer number (9909929911).

Almost surely, 2^19819859821 is an apocalyptic number.

It is an amenable number.

19819859821 is a deficient number, since it is larger than the sum of its proper divisors (1).

19819859821 is an equidigital number, since it uses as much as digits as its factorization.

19819859821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3732480, while the sum is 61.

The spelling of 19819859821 in words is "nineteen billion, eight hundred nineteen million, eight hundred fifty-nine thousand, eight hundred twenty-one".