1991181 has 16 divisors (see below), whose sum is σ = 2824640. Its totient is φ = 1244160.

The previous prime is 1991177. The next prime is 1991189. The reversal of 1991181 is 1811991.

It is a happy number.

It is not a de Polignac number, because 1991181 - 2² = 1991177 is a prime.

It is a super-2 number, since 2×1991181² = 7929603549522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991189) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10221 + ... + 10413.

It is an arithmetic number, because the mean of its divisors is an integer number (176540).

2^1991181 is an apocalyptic number.

It is an amenable number.

1991181 is a deficient number, since it is larger than the sum of its proper divisors (833459).

1991181 is a wasteful number, since it uses less digits than its factorization.

1991181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 396.

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

The square root of 1991181 is about 1411.0921302310. The cubic root of 1991181 is about 125.8066447305.

The spelling of 1991181 in words is "one million, nine hundred ninety-one thousand, one hundred eighty-one".