11991509 has 4 divisors (see below), whose sum is σ = 12002016. Its totient is φ = 11981004.

The previous prime is 11991481. The next prime is 11991517. The reversal of 11991509 is 90519911.

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 a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 90519911 = 389 ⋅232699.

It is a cyclic number.

It is not a de Polignac number, because 11991509 - 2⁸ = 11991253 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 (11991209) 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, 3299 + ... + 5904.

It is an arithmetic number, because the mean of its divisors is an integer number (3000504).

Almost surely, 2^11991509 is an apocalyptic number.

It is an amenable number.

11991509 is a deficient number, since it is larger than the sum of its proper divisors (10507).

11991509 is an equidigital number, since it uses as much as digits as its factorization.

11991509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10506.

The product of its (nonzero) digits is 3645, while the sum is 35.

The square root of 11991509 is about 3462.8758279788. The cubic root of 11991509 is about 228.8888370548. Note that the first 4 decimals are identical.

The spelling of 11991509 in words is "eleven million, nine hundred ninety-one thousand, five hundred nine".