1991331 has 16 divisors (see below), whose sum is σ = 2977920. Its totient is φ = 1315080.

The previous prime is 1991293. The next prime is 1991351. The reversal of 1991331 is 1331991.

It is not a de Polignac number, because 1991331 - 2⁶ = 1991267 is a prime.

It is a super-2 number, since 2×1991331² = 7930798303122, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 1991295 and 1991304.

It is not an unprimeable number, because it can be changed into a prime (1991351) 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 15 ways as a sum of consecutive naturals, for example, 3256 + ... + 3818.

It is an arithmetic number, because the mean of its divisors is an integer number (186120).

2^1991331 is an apocalyptic number.

1991331 is a deficient number, since it is larger than the sum of its proper divisors (986589).

1991331 is a wasteful number, since it uses less digits than its factorization.

1991331 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 703 (or 697 counting only the distinct ones).

The product of its digits is 729, while the sum is 27.

The square root of 1991331 is about 1411.1452795513. The cubic root of 1991331 is about 125.8098037473.

The spelling of 1991331 in words is "one million, nine hundred ninety-one thousand, three hundred thirty-one".