11721981 has 4 divisors (see below), whose sum is σ = 15629312. Its totient is φ = 7814652.

The previous prime is 11721971. The next prime is 11721991. The reversal of 11721981 is 18912711.

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.

It is an interprime number because it is at equal distance from previous prime (11721971) and next prime (11721991).

It is not a de Polignac number, because 11721981 - 2⁵ = 11721949 is a prime.

It is a super-2 number, since 2×11721981² = 274809677128722, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (11721911) 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, 1953661 + ... + 1953666.

It is an arithmetic number, because the mean of its divisors is an integer number (3907328).

Almost surely, 2^11721981 is an apocalyptic number.

It is an amenable number.

11721981 is a deficient number, since it is larger than the sum of its proper divisors (3907331).

11721981 is an equidigital number, since it uses as much as digits as its factorization.

11721981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3907330.

The product of its digits is 1008, while the sum is 30.

The square root of 11721981 is about 3423.7378696390. The cubic root of 11721981 is about 227.1609472672.

The spelling of 11721981 in words is "eleven million, seven hundred twenty-one thousand, nine hundred eighty-one".