1991813 has 4 divisors (see below), whose sum is σ = 2034240. Its totient is φ = 1949388.

The previous prime is 1991797. The next prime is 1991819. The reversal of 1991813 is 3181991.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 3181991 = 193 ⋅16487.

It is a cyclic number.

It is not a de Polignac number, because 1991813 - 2⁴ = 1991797 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1991813.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991819) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21143 + ... + 21236.

It is an arithmetic number, because the mean of its divisors is an integer number (508560).

2^1991813 is an apocalyptic number.

It is an amenable number.

1991813 is a deficient number, since it is larger than the sum of its proper divisors (42427).

1991813 is an equidigital number, since it uses as much as digits as its factorization.

1991813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42426.

The product of its digits is 1944, while the sum is 32.

The square root of 1991813 is about 1411.3160524843. The cubic root of 1991813 is about 125.8199536476.

The spelling of 1991813 in words is "one million, nine hundred ninety-one thousand, eight hundred thirteen".