11521981 has 4 divisors (see below), whose sum is σ = 11592832. Its totient is φ = 11451132.

The previous prime is 11521967. The next prime is 11521997. The reversal of 11521981 is 18912511.

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: 18912511 = 31 ⋅610081.

It is a cyclic number.

It is not a de Polignac number, because 11521981 - 2⁵ = 11521949 is a prime.

It is a super-2 number, since 2×11521981² = 265512092328722, 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 (11521921) 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, 35181 + ... + 35506.

It is an arithmetic number, because the mean of its divisors is an integer number (2898208).

Almost surely, 2^11521981 is an apocalyptic number.

It is an amenable number.

11521981 is a deficient number, since it is larger than the sum of its proper divisors (70851).

11521981 is an equidigital number, since it uses as much as digits as its factorization.

11521981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 70850.

The product of its digits is 720, while the sum is 28.

The square root of 11521981 is about 3394.4043660118. The cubic root of 11521981 is about 225.8615919698.

The spelling of 11521981 in words is "eleven million, five hundred twenty-one thousand, nine hundred eighty-one".