217805989 has 4 divisors (see below), whose sum is σ = 230618124. Its totient is φ = 204993856.

The previous prime is 217805977. The next prime is 217805999. The reversal of 217805989 is 989508712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 100841764 + 116964225 = 10042^2 + 10815^2 .

It is a cyclic number.

It is not a de Polignac number, because 217805989 - 2¹⁷ = 217674917 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (217805999) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6406042 + ... + 6406075.

It is an arithmetic number, because the mean of its divisors is an integer number (57654531).

Almost surely, 2^217805989 is an apocalyptic number.

It is an amenable number.

217805989 is a deficient number, since it is larger than the sum of its proper divisors (12812135).

217805989 is a wasteful number, since it uses less digits than its factorization.

217805989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12812134.

The product of its (nonzero) digits is 362880, while the sum is 49.

The square root of 217805989 is about 14758.2515563328. The cubic root of 217805989 is about 601.6675730767.

The spelling of 217805989 in words is "two hundred seventeen million, eight hundred five thousand, nine hundred eighty-nine".