Data commit

Task/Attractive-numbers/F-Sharp/attractive-numbers.fs

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+// attractive_numbers.fsx
+// taken from Primality by trial division
+let rec primes =
+    let next_state s = Some(s, s + 2)
+    Seq.cache
+        (Seq.append
+            (seq[ 2; 3; 5 ])
+            (Seq.unfold next_state 7
+            |> Seq.filter is_prime))
+and is_prime number =
+    let rec is_prime_core number current limit =
+        let cprime = primes |> Seq.item current
+        if cprime >= limit then true
+        elif number % cprime = 0 then false
+        else is_prime_core number (current + 1) (number/cprime)
+    if number = 2 then true
+    elif number < 2 then false
+    else is_prime_core number 0 number
+
+// taken from Prime decomposition task and modified to add
+let count_prime_divisors n =
+    let rec loop c n count =
+        let p = Seq.item n primes
+        if c < (p * p) then count
+        elif c % p = 0 then loop (c / p) n (count + 1)
+        else loop c (n + 1) count
+    loop n 0 1
+
+let is_attractive = count_prime_divisors >> is_prime
+let print_iter i n =
+    if i % 10 = 9
+    then printfn "%d" n
+    else printf "%d\t" n
+
+[1..120]
+|> List.filter is_attractive
+|> List.iteri print_iter