199987721 has 2 divisors, whose sum is σ = 199987722. Its totient is φ = 199987720.

The previous prime is 199987657. The next prime is 199987729. The reversal of 199987721 is 127789991.

199987721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 176358400 + 23629321 = 13280^2 + 4861^2 .

It is a cyclic number.

It is not a de Polignac number, because 199987721 - 2⁶ = 199987657 is a prime.

It is not a weakly prime, because it can be changed into another prime (199987729) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 99993860 + 99993861.

It is an arithmetic number, because the mean of its divisors is an integer number (99993861).

Almost surely, 2^199987721 is an apocalyptic number.

It is an amenable number.

199987721 is a deficient number, since it is larger than the sum of its proper divisors (1).

199987721 is an equidigital number, since it uses as much as digits as its factorization.

199987721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 571536, while the sum is 53.

The square root of 199987721 is about 14141.7014888591. The cubic root of 199987721 is about 584.7915793930.

The spelling of 199987721 in words is "one hundred ninety-nine million, nine hundred eighty-seven thousand, seven hundred twenty-one".