1155991 has 8 divisors (see below), whose sum is σ = 1200800. Its totient is φ = 1111968.

The previous prime is 1155977. The next prime is 1155997. The reversal of 1155991 is 1995511.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1155991 - 2⁷ = 1155863 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1155997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5710 + ... + 5908.

It is an arithmetic number, because the mean of its divisors is an integer number (150100).

2^1155991 is an apocalyptic number.

1155991 is a deficient number, since it is larger than the sum of its proper divisors (44809).

1155991 is a wasteful number, since it uses less digits than its factorization.

1155991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 393.

The product of its digits is 2025, while the sum is 31.

The square root of 1155991 is about 1075.1702190816. The cubic root of 1155991 is about 104.9505738653.

Subtracting from 1155991 its sum of digits (31), we obtain a triangular number (1155960 = T₁₅₂₀).

It can be divided in two parts, 115599 and 1, that added together give a square (115600 = 340²).

The spelling of 1155991 in words is "one million, one hundred fifty-five thousand, nine hundred ninety-one".