11531981 has 4 divisors (see below), whose sum is σ = 11622912. Its totient is φ = 11441052.

The previous prime is 11531977. The next prime is 11531987. The reversal of 11531981 is 18913511.

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: 18913511 = 929 ⋅20359.

It is a cyclic number.

It is not a de Polignac number, because 11531981 - 2² = 11531977 is a prime.

It is a super-2 number, since 2×11531981² = 265973171568722, 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 (11531987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 45275 + ... + 45528.

It is an arithmetic number, because the mean of its divisors is an integer number (2905728).

Almost surely, 2^11531981 is an apocalyptic number.

It is an amenable number.

11531981 is a deficient number, since it is larger than the sum of its proper divisors (90931).

11531981 is an equidigital number, since it uses as much as digits as its factorization.

11531981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 90930.

The product of its digits is 1080, while the sum is 29.

The square root of 11531981 is about 3395.8770590232. The cubic root of 11531981 is about 225.9269153088.

The spelling of 11531981 in words is "eleven million, five hundred thirty-one thousand, nine hundred eighty-one".