991909 has 2 divisors, whose sum is σ = 991910. Its totient is φ = 991908.

The previous prime is 991901. The next prime is 991927. The reversal of 991909 is 909199.

991909 is digitally balanced in base 2, 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., 792100 + 199809 = 890^2 + 447^2 .

It is a cyclic number.

It is not a de Polignac number, because 991909 - 2³ = 991901 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495954 + 495955.

It is an arithmetic number, because the mean of its divisors is an integer number (495955).

2⁹⁹¹⁹⁰⁹ is an apocalyptic number.

It is an amenable number.

991909 is a deficient number, since it is larger than the sum of its proper divisors (1).

991909 is an equidigital number, since it uses as much as digits as its factorization.

991909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6561, while the sum is 37.

The square root of 991909 is about 995.9462836920. The cubic root of 991909 is about 99.7295693318.

It can be divided in two parts, 99190 and 9, that added together give a palindrome (99199).

The spelling of 991909 in words is "nine hundred ninety-one thousand, nine hundred nine".