11991561 has 8 divisors (see below), whose sum is σ = 16008384. Its totient is φ = 7984560.

The previous prime is 11991523. The next prime is 11991583. The reversal of 11991561 is 16519911.

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

It is not a de Polignac number, because 11991561 - 2⁷ = 11991433 is a prime.

It is a Smith number, since the sum of its digits (33) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (11991461) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1155 + ... + 5031.

It is an arithmetic number, because the mean of its divisors is an integer number (2001048).

Almost surely, 2^11991561 is an apocalyptic number.

It is an amenable number.

11991561 is a deficient number, since it is larger than the sum of its proper divisors (4016823).

11991561 is a wasteful number, since it uses less digits than its factorization.

11991561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4911.

The product of its digits is 2430, while the sum is 33.

The square root of 11991561 is about 3462.8833361810. The cubic root of 11991561 is about 228.8891679057.

The spelling of 11991561 in words is "eleven million, nine hundred ninety-one thousand, five hundred sixty-one".