991609 has 4 divisors (see below), whose sum is σ = 993616. Its totient is φ = 989604.

The previous prime is 991607. The next prime is 991619. The reversal of 991609 is 906199.

It is a happy number.

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: 906199 = 7 ⋅129457.

It is a cyclic number.

It is not a de Polignac number, because 991609 - 2¹ = 991607 is a prime.

It is a Duffinian number.

991609 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (991603) 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, 322 + ... + 1444.

It is an arithmetic number, because the mean of its divisors is an integer number (248404).

2⁹⁹¹⁶⁰⁹ is an apocalyptic number.

It is an amenable number.

991609 is a deficient number, since it is larger than the sum of its proper divisors (2007).

991609 is a wasteful number, since it uses less digits than its factorization.

991609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2006.

The product of its (nonzero) digits is 4374, while the sum is 34.

The square root of 991609 is about 995.7956617700. The cubic root of 991609 is about 99.7195140117.

It can be divided in two parts, 991 and 609, that added together give a square (1600 = 40²).

The spelling of 991609 in words is "nine hundred ninety-one thousand, six hundred nine".