43991809 has 2 divisors, whose sum is σ = 43991810. Its totient is φ = 43991808.

The previous prime is 43991807. The next prime is 43991851. The reversal of 43991809 is 90819934.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 35141184 + 8850625 = 5928^2 + 2975^2 .

It is a cyclic number.

It is not a de Polignac number, because 43991809 - 2¹ = 43991807 is a prime.

Together with 43991807, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (43991807) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 21995904 + 21995905.

It is an arithmetic number, because the mean of its divisors is an integer number (21995905).

Almost surely, 2^43991809 is an apocalyptic number.

It is an amenable number.

43991809 is a deficient number, since it is larger than the sum of its proper divisors (1).

43991809 is an equidigital number, since it uses as much as digits as its factorization.

43991809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 69984, while the sum is 43.

The square root of 43991809 is about 6632.6321321177. The cubic root of 43991809 is about 353.0129252919.

The spelling of 43991809 in words is "forty-three million, nine hundred ninety-one thousand, eight hundred nine".