Data commit

Task/Weird-numbers/Nim/weird-numbers.nim

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+import algorithm, math, strutils
+
+func divisors(n: int): seq[int] =
+  var smallDivs = @[1]
+  for i in 2..sqrt(n.toFloat).int:
+    if n mod i == 0:
+      let j = n div i
+      smallDivs.add i
+      if i != j: result.add j
+  result.add reversed(smallDivs)
+
+func abundant(n: int; divs: seq[int]): bool {.inline.}=
+  sum(divs) > n
+
+func semiperfect(n: int; divs: seq[int]): bool =
+  if divs.len > 0:
+    let h = divs[0]
+    let t = divs[1..^1]
+    result = if n < h: semiperfect(n, t)
+             else: n == h or semiperfect(n - h, t) or semiperfect(n, t)
+
+func sieve(limit: int): seq[bool] =
+  # False denotes abundant and not semi-perfect.
+  # Only interested in even numbers >= 2.
+  result.setLen(limit)
+  for i in countup(2, limit - 1, 2):
+    if result[i]: continue
+    let divs = divisors(i)
+    if not abundant(i, divs):
+      result[i] = true
+    elif semiperfect(i, divs):
+      for j in countup(i, limit - 1, i):
+        result[j] = true
+
+
+const Max = 25
+let w = sieve(17_000)
+var list: seq[int]
+
+echo "The first 25 weird numbers are:"
+var n = 2
+while list.len != Max:
+  if not w[n]: list.add n
+  inc n, 2
+echo list.join(" ")