43781 has 2 divisors, whose sum is σ = 43782.
Its totient is φ = 43780.
The previous prime is 43777. The next prime is 43783. The reversal of 43781 is 18734.
It is a happy number.
It is a strong prime.
It can be written as a sum of positive squares in only one way, i.e., 43681 + 100 = 209^2 + 10^2
It is a cyclic number.
It is not a de Polignac number, because 43781 - 22 = 43777 is a prime.
It is a super-2 number, since 2×437812 = 3833551922, which contains 22 as substring.
Together with 43783, it forms a pair of twin primes.
It is a Chen prime.
It is equal to p4559 and since 43781 and 4559 have the same sum of digits, it is a Honaker prime.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (43783) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (7) of ones.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 21890 + 21891.
It is an arithmetic number, because the mean of its divisors is an integer number (21891).
243781 is an apocalyptic number.
It is an amenable number.
43781 is a deficient number, since it is larger than the sum of its proper divisors (1).
43781 is an equidigital number, since it uses as much as digits as its factorization.
43781 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 672, while the sum is 23.
The square root of 43781 is about 209.2390976849.
The cubic root of 43781 is about 35.2448142196.
The spelling of 43781 in words is "forty-three thousand, seven hundred eighty-one".