1991009803 has 4 divisors (see below), whose sum is σ = 1991313280. Its totient is φ = 1990706328.

The previous prime is 1991009777. The next prime is 1991009821. The reversal of 1991009803 is 3089001991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 3089001991 = 257 ⋅12019463.

It is a cyclic number.

It is not a de Polignac number, because 1991009803 - 2⁹ = 1991009291 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991009843) 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, 141675 + ... + 155092.

It is an arithmetic number, because the mean of its divisors is an integer number (497828320).

Almost surely, 2^1991009803 is an apocalyptic number.

1991009803 is a deficient number, since it is larger than the sum of its proper divisors (303477).

1991009803 is an equidigital number, since it uses as much as digits as its factorization.

1991009803 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 303476.

The product of its (nonzero) digits is 17496, while the sum is 40.

The square root of 1991009803 is about 44620.7328828203. The cubic root of 1991009803 is about 1258.0303910857.

The spelling of 1991009803 in words is "one billion, nine hundred ninety-one million, nine thousand, eight hundred three".