1181991 has 4 divisors (see below), whose sum is σ = 1575992. Its totient is φ = 787992.

The previous prime is 1181987. The next prime is 1182007. The reversal of 1181991 is 1991811.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1991811 = 3 ⋅663937.

It is not a de Polignac number, because 1181991 - 2² = 1181987 is a prime.

It is a D-number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1181911) 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, 196996 + ... + 197001.

It is an arithmetic number, because the mean of its divisors is an integer number (393998).

2^1181991 is an apocalyptic number.

1181991 is a deficient number, since it is larger than the sum of its proper divisors (394001).

1181991 is an equidigital number, since it uses as much as digits as its factorization.

1181991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 394000.

The product of its digits is 648, while the sum is 30.

The square root of 1181991 is about 1087.1940949067. The cubic root of 1181991 is about 105.7315802690.

The spelling of 1181991 in words is "one million, one hundred eighty-one thousand, nine hundred ninety-one".