991209 has 8 divisors (see below), whose sum is σ = 1331680. Its totient is φ = 655776.

The previous prime is 991201. The next prime is 991217. The reversal of 991209 is 902199.

It is an interprime number because it is at equal distance from previous prime (991201) and next prime (991217).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 991209 - 2³ = 991201 is a prime.

It is a Duffinian number.

991209 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (991201) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 772 + ... + 1605.

It is an arithmetic number, because the mean of its divisors is an integer number (166460).

2⁹⁹¹²⁰⁹ is an apocalyptic number.

It is an amenable number.

991209 is a deficient number, since it is larger than the sum of its proper divisors (340471).

991209 is a wasteful number, since it uses less digits than its factorization.

991209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2519.

The product of its (nonzero) digits is 1458, while the sum is 30.

The square root of 991209 is about 995.5947970937. The cubic root of 991209 is about 99.7061037629.

The spelling of 991209 in words is "nine hundred ninety-one thousand, two hundred nine".