1991509723 has 4 divisors (see below), whose sum is σ = 2276011120. Its totient is φ = 1707008328.

The previous prime is 1991509661. The next prime is 1991509759. The reversal of 1991509723 is 3279051991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 3279051991 = 2851 ⋅1150141.

It is a cyclic number.

It is not a de Polignac number, because 1991509723 - 2²⁵ = 1957955291 is a prime.

It is a super-2 number, since 2×1991509723² = 7932221953607073458, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991500723) 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, 142250688 + ... + 142250701.

It is an arithmetic number, because the mean of its divisors is an integer number (569002780).

Almost surely, 2^1991509723 is an apocalyptic number.

1991509723 is a deficient number, since it is larger than the sum of its proper divisors (284501397).

1991509723 is an equidigital number, since it uses as much as digits as its factorization.

1991509723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 284501396.

The product of its (nonzero) digits is 153090, while the sum is 46.

The square root of 1991509723 is about 44626.3344114212. The cubic root of 1991509723 is about 1258.1356746662.

The spelling of 1991509723 in words is "one billion, nine hundred ninety-one million, five hundred nine thousand, seven hundred twenty-three".