1991671081 has 4 divisors (see below), whose sum is σ = 1998709072. Its totient is φ = 1984633092.

The previous prime is 1991671079. The next prime is 1991671109. The reversal of 1991671081 is 1801761991.

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: 1801761991 = 9803 ⋅183797.

It is a cyclic number.

It is not a de Polignac number, because 1991671081 - 2¹ = 1991671079 is a prime.

It is a super-2 number, since 2×1991671081² = 7933507389783417122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991671001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3518571 + ... + 3519136.

It is an arithmetic number, because the mean of its divisors is an integer number (499677268).

Almost surely, 2^1991671081 is an apocalyptic number.

It is an amenable number.

1991671081 is a deficient number, since it is larger than the sum of its proper divisors (7037991).

1991671081 is an equidigital number, since it uses as much as digits as its factorization.

1991671081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7037990.

The product of its (nonzero) digits is 27216, while the sum is 43.

The square root of 1991671081 is about 44628.1422535153. The cubic root of 1991671081 is about 1258.1696530380.

The spelling of 1991671081 in words is "one billion, nine hundred ninety-one million, six hundred seventy-one thousand, eighty-one".