1919999891 has 4 divisors (see below), whose sum is σ = 1928384400. Its totient is φ = 1911615384.

The previous prime is 1919999857. The next prime is 1919999903. The reversal of 1919999891 is 1989999191.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1919999891 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1919999591) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4191911 + ... + 4192368.

It is an arithmetic number, because the mean of its divisors is an integer number (482096100).

Almost surely, 2^1919999891 is an apocalyptic number.

1919999891 is a deficient number, since it is larger than the sum of its proper divisors (8384509).

1919999891 is an equidigital number, since it uses as much as digits as its factorization.

1919999891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8384508.

The product of its digits is 4251528, while the sum is 65.

The square root of 1919999891 is about 43817.8033566266. The cubic root of 1919999891 is about 1242.8929788615.

The spelling of 1919999891 in words is "one billion, nine hundred nineteen million, nine hundred ninety-nine thousand, eight hundred ninety-one".