243991891 has 12 divisors (see below), whose sum is σ = 288225000. Its totient is φ = 204746880.

The previous prime is 243991883. The next prime is 243991897. The reversal of 243991891 is 198199342.

It is a happy number.

It is not a de Polignac number, because 243991891 - 2³ = 243991883 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (243991897) 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 in 11 ways as a sum of consecutive naturals, for example, 63766 + ... + 67483.

It is an arithmetic number, because the mean of its divisors is an integer number (24018750).

Almost surely, 2^243991891 is an apocalyptic number.

243991891 is a deficient number, since it is larger than the sum of its proper divisors (44233109).

243991891 is a wasteful number, since it uses less digits than its factorization.

243991891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 131286 (or 131273 counting only the distinct ones).

The product of its digits is 139968, while the sum is 46.

The square root of 243991891 is about 15620.2397868919. The cubic root of 243991891 is about 624.8730545375.

The spelling of 243991891 in words is "two hundred forty-three million, nine hundred ninety-one thousand, eight hundred ninety-one".