19909999 has 4 divisors (see below), whose sum is σ = 20333664. Its totient is φ = 19486336.

The previous prime is 19909997. The next prime is 19910017. The reversal of 19909999 is 99990991.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 99990991 = 17 ⋅5881823.

It is a cyclic number.

It is not a de Polignac number, because 19909999 - 2¹ = 19909997 is a prime.

It is a Duffinian number.

19909999 is a modest number, since divided by 9999 gives 1990 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19909993) 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 in 3 ways as a sum of consecutive naturals, for example, 211762 + ... + 211855.

It is an arithmetic number, because the mean of its divisors is an integer number (5083416).

Almost surely, 2^19909999 is an apocalyptic number.

19909999 is a deficient number, since it is larger than the sum of its proper divisors (423665).

19909999 is an equidigital number, since it uses as much as digits as its factorization.

19909999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 423664.

The product of its (nonzero) digits is 531441, while the sum is 55.

The square root of 19909999 is about 4462.0621914088. The cubic root of 19909999 is about 271.0339822039.

The spelling of 19909999 in words is "nineteen million, nine hundred nine thousand, nine hundred ninety-nine".