11981561 has 4 divisors (see below), whose sum is σ = 12076032. Its totient is φ = 11887092.

The previous prime is 11981443. The next prime is 11981587. The reversal of 11981561 is 16518911.

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: 16518911 = 2129 ⋅7759.

It is a cyclic number.

It is not a de Polignac number, because 11981561 - 2¹⁰ = 11980537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (11981161) 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, 47045 + ... + 47298.

It is an arithmetic number, because the mean of its divisors is an integer number (3019008).

Almost surely, 2^11981561 is an apocalyptic number.

It is an amenable number.

11981561 is a deficient number, since it is larger than the sum of its proper divisors (94471).

11981561 is an equidigital number, since it uses as much as digits as its factorization.

11981561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 94470.

The product of its digits is 2160, while the sum is 32.

The square root of 11981561 is about 3461.4391515669. The cubic root of 11981561 is about 228.8255251427.

The spelling of 11981561 in words is "eleven million, nine hundred eighty-one thousand, five hundred sixty-one".