1991615 has 4 divisors (see below), whose sum is σ = 2389944. Its totient is φ = 1593288.

The previous prime is 1991609. The next prime is 1991617. The reversal of 1991615 is 5161991.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 5161991 = 197 ⋅26203.

It is a cyclic number.

It is not a de Polignac number, because 1991615 - 2⁶ = 1991551 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991617) 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, 199157 + ... + 199166.

It is an arithmetic number, because the mean of its divisors is an integer number (597486).

2^1991615 is an apocalyptic number.

1991615 is a deficient number, since it is larger than the sum of its proper divisors (398329).

1991615 is an equidigital number, since it uses as much as digits as its factorization.

1991615 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 398328.

The product of its digits is 2430, while the sum is 32.

The square root of 1991615 is about 1411.2459034484. The cubic root of 1991615 is about 125.8157843847.

The spelling of 1991615 in words is "one million, nine hundred ninety-one thousand, six hundred fifteen".