11991781 has 2 divisors, whose sum is σ = 11991782. Its totient is φ = 11991780.

The previous prime is 11991773. The next prime is 11991839. The reversal of 11991781 is 18719911.

11991781 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11937025 + 54756 = 3455^2 + 234^2 .

It is a cyclic number.

It is not a de Polignac number, because 11991781 - 2³ = 11991773 is a prime.

It is a super-2 number, since 2×11991781² = 287605623103922, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 11991781.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (11991731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5995890 + 5995891.

It is an arithmetic number, because the mean of its divisors is an integer number (5995891).

Almost surely, 2^11991781 is an apocalyptic number.

It is an amenable number.

11991781 is a deficient number, since it is larger than the sum of its proper divisors (1).

11991781 is an equidigital number, since it uses as much as digits as its factorization.

11991781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4536, while the sum is 37.

The square root of 11991781 is about 3462.9151014716. The cubic root of 11991781 is about 228.8905676486.

The spelling of 11991781 in words is "eleven million, nine hundred ninety-one thousand, seven hundred eighty-one".