11721781 has 2 divisors, whose sum is σ = 11721782. Its totient is φ = 11721780.

The previous prime is 11721779. The next prime is 11721791. The reversal of 11721781 is 18712711.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 6081156 + 5640625 = 2466^2 + 2375^2 .

It is an emirp because it is prime and its reverse (18712711) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 11721781 - 2¹ = 11721779 is a prime.

It is a super-2 number, since 2×11721781² = 274800299623922, which contains 22 as substring.

Together with 11721779, it forms a pair of twin primes.

It is a zygodrome in base 5.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (11721791) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5860890 + 5860891.

It is an arithmetic number, because the mean of its divisors is an integer number (5860891).

Almost surely, 2^11721781 is an apocalyptic number.

It is an amenable number.

11721781 is a deficient number, since it is larger than the sum of its proper divisors (1).

11721781 is an equidigital number, since it uses as much as digits as its factorization.

11721781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 784, while the sum is 28.

The square root of 11721781 is about 3423.7086616708. The cubic root of 11721781 is about 227.1596553226.

The spelling of 11721781 in words is "eleven million, seven hundred twenty-one thousand, seven hundred eighty-one".