1991815 has 8 divisors (see below), whose sum is σ = 2731680. Its totient is φ = 1365792.

The previous prime is 1991797. The next prime is 1991819. The reversal of 1991815 is 5181991.

1991815 = T₄₂₅ + T₄₂₆ + ... + T₄₄₅.

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 1991815 - 2¹⁵ = 1959047 is a prime.

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 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, 28420 + ... + 28489.

It is an arithmetic number, because the mean of its divisors is an integer number (341460).

2^1991815 is an apocalyptic number.

1991815 is a deficient number, since it is larger than the sum of its proper divisors (739865).

1991815 is an equidigital number, since it uses as much as digits as its factorization.

1991815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 56921.

The product of its digits is 3240, while the sum is 34.

The square root of 1991815 is about 1411.3167610427. The cubic root of 1991815 is about 125.8199957600.

The spelling of 1991815 in words is "one million, nine hundred ninety-one thousand, eight hundred fifteen".