19990865 has 4 divisors (see below), whose sum is σ = 23989044. Its totient is φ = 15992688.

The previous prime is 19990849. The next prime is 19990879. The reversal of 19990865 is 56809991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 56809991 = 7 ⋅8115713.

It can be written as a sum of positive squares in 2 ways, for example, as 7059649 + 12931216 = 2657^2 + 3596^2 .

It is a cyclic number.

It is not a de Polignac number, because 19990865 - 2⁴ = 19990849 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1999082 + ... + 1999091.

It is an arithmetic number, because the mean of its divisors is an integer number (5997261).

Almost surely, 2^19990865 is an apocalyptic number.

It is an amenable number.

19990865 is a deficient number, since it is larger than the sum of its proper divisors (3998179).

19990865 is an equidigital number, since it uses as much as digits as its factorization.

19990865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3998178.

The product of its (nonzero) digits is 174960, while the sum is 47.

The square root of 19990865 is about 4471.1145143018. The cubic root of 19990865 is about 271.4004283576.

The spelling of 19990865 in words is "nineteen million, nine hundred ninety thousand, eight hundred sixty-five".