1991388673 has 4 divisors (see below), whose sum is σ = 2021110960. Its totient is φ = 1961666388.

The previous prime is 1991388667. The next prime is 1991388677. The reversal of 1991388673 is 3768831991.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 3768831991 = 61 ⋅61784131.

It is a cyclic number.

It is not a de Polignac number, because 1991388673 - 2²⁹ = 1454517761 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991388677) 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, 14861043 + ... + 14861176.

It is an arithmetic number, because the mean of its divisors is an integer number (505277740).

Almost surely, 2^1991388673 is an apocalyptic number.

It is an amenable number.

1991388673 is a deficient number, since it is larger than the sum of its proper divisors (29722287).

1991388673 is an equidigital number, since it uses as much as digits as its factorization.

1991388673 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29722286.

The product of its digits is 1959552, while the sum is 55.

The square root of 1991388673 is about 44624.9781288462. The cubic root of 1991388673 is about 1258.1101830492.

The spelling of 1991388673 in words is "one billion, nine hundred ninety-one million, three hundred eighty-eight thousand, six hundred seventy-three".