1991321 has 4 divisors (see below), whose sum is σ = 2009700. Its totient is φ = 1972944.

The previous prime is 1991293. The next prime is 1991351. The reversal of 1991321 is 1231991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1231991 = 307 ⋅4013.

It can be written as a sum of positive squares in 2 ways, for example, as 1413721 + 577600 = 1189^2 + 760^2 .

It is a cyclic number.

It is not a de Polignac number, because 1991321 - 2¹⁴ = 1974937 is a prime.

It is a Duffinian number.

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 3 ways as a sum of consecutive naturals, for example, 9026 + ... + 9243.

It is an arithmetic number, because the mean of its divisors is an integer number (502425).

2^1991321 is an apocalyptic number.

It is an amenable number.

1991321 is a deficient number, since it is larger than the sum of its proper divisors (18379).

1991321 is a wasteful number, since it uses less digits than its factorization.

1991321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18378.

The product of its digits is 486, while the sum is 26.

The square root of 1991321 is about 1411.1417363256. The cubic root of 1991321 is about 125.8095931511.

The spelling of 1991321 in words is "one million, nine hundred ninety-one thousand, three hundred twenty-one".