1991263 has 4 divisors (see below), whose sum is σ = 2028888. Its totient is φ = 1953640.

The previous prime is 1991251. The next prime is 1991267. The reversal of 1991263 is 3621991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 3621991 = 181 ⋅20011.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1991263 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an Ulam 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 (1991267) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 18733 + ... + 18838.

It is an arithmetic number, because the mean of its divisors is an integer number (507222).

2^1991263 is an apocalyptic number.

1991263 is a deficient number, since it is larger than the sum of its proper divisors (37625).

1991263 is an equidigital number, since it uses as much as digits as its factorization.

1991263 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37624.

The product of its digits is 2916, while the sum is 31.

The square root of 1991263 is about 1411.1211854409. The cubic root of 1991263 is about 125.8083716793.

The spelling of 1991263 in words is "one million, nine hundred ninety-one thousand, two hundred sixty-three".