199920821 has 2 divisors, whose sum is σ = 199920822. Its totient is φ = 199920820.

The previous prime is 199920769. The next prime is 199920839. The reversal of 199920821 is 128029991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 180902500 + 19018321 = 13450^2 + 4361^2 .

It is an emirp because it is prime and its reverse (128029991) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 199920821 - 2¹⁴ = 199904437 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (199920841) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 99960410 + 99960411.

It is an arithmetic number, because the mean of its divisors is an integer number (99960411).

Almost surely, 2^199920821 is an apocalyptic number.

It is an amenable number.

199920821 is a deficient number, since it is larger than the sum of its proper divisors (1).

199920821 is an equidigital number, since it uses as much as digits as its factorization.

199920821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 23328, while the sum is 41.

The square root of 199920821 is about 14139.3359462176. The cubic root of 199920821 is about 584.7263638560.

The spelling of 199920821 in words is "one hundred ninety-nine million, nine hundred twenty thousand, eight hundred twenty-one".