11581981 has 4 divisors (see below), whose sum is σ = 12263292. Its totient is φ = 10900672.

The previous prime is 11581979. The next prime is 11581987. The reversal of 11581981 is 18918511.

11581981 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18918511 = 2887 ⋅6553.

It can be written as a sum of positive squares in 2 ways, for example, as 4644025 + 6937956 = 2155^2 + 2634^2 .

It is not a de Polignac number, because 11581981 - 2¹ = 11581979 is a prime.

It is a super-2 number, since 2×11581981² = 268284567768722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (11581987) 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, 340630 + ... + 340663.

It is an arithmetic number, because the mean of its divisors is an integer number (3065823).

Almost surely, 2^11581981 is an apocalyptic number.

It is an amenable number.

11581981 is a deficient number, since it is larger than the sum of its proper divisors (681311).

11581981 is an equidigital number, since it uses as much as digits as its factorization.

11581981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 681310.

The product of its digits is 2880, while the sum is 34.

The square root of 11581981 is about 3403.2309648333. The cubic root of 11581981 is about 226.2529668018.

The spelling of 11581981 in words is "eleven million, five hundred eighty-one thousand, nine hundred eighty-one".