From b70ff262a69b0e90223ebcc47eafad7c9d6eb324 Mon Sep 17 00:00:00 2001
From: jaseg <git@jaseg.de>
Date: Mon, 8 Dec 2025 14:56:49 +0100
Subject: [PATCH] Improve cofactor calculation

---
 src/kicoil/cli.py      | 7 +++----
 src/kicoil/geometry.py | 6 +++---
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/src/kicoil/cli.py b/src/kicoil/cli.py
index d9dd55f..6027a03 100644
--- a/src/kicoil/cli.py
+++ b/src/kicoil/cli.py
@@ -11,7 +11,7 @@ import warnings
 import click
 from gerbonara.layers import LayerStack
 
-from .geometry import PlanarInductor
+from .geometry import PlanarInductor, divisors
 from .kicad import footprint_to_board
 from .svg import make_transparent_svg
 
@@ -20,11 +20,10 @@ def print_valid_twists(ctx, param, value):
     if not value or ctx.resilient_parsing:
         return
 
-    print(f'Valid twist counts for {value} turns:', file=sys.stderr)
+    click.echo(f'Valid twist counts for {value} turns:', file=sys.stderr)
     for d in divisors(value, value):
-        print(f'  {d}', file=sys.stderr)
+        click.echo(f'  {d}', file=sys.stderr)
 
-    click.echo()
     ctx.exit()
 
 
diff --git a/src/kicoil/geometry.py b/src/kicoil/geometry.py
index d691dff..874d30e 100644
--- a/src/kicoil/geometry.py
+++ b/src/kicoil/geometry.py
@@ -56,9 +56,9 @@ def farey_sequence(n: int, descending: bool = False) -> None:
 
 def divisors(n, max_b=10):
     for a, b in farey_sequence(n):
-        if a == n and b < max_b:
+        if a != 0 and a == n and b < max_b:
             yield b
-        if b == n and a < max_b:
+        if b != 1 and b == n and a < max_b:
             yield a
 
 
@@ -161,7 +161,7 @@ class PlanarInductor():
         if gcd(self.twists, self.turns) != 1:
             raise ValueError(f'For the geometry to work out, the twists parameter must be co-prime to turns, i.e. the two must have 1 as their greatest common divisor. You can print valid values for twists by running the kicoil CLI with --show-twists [turns number].\n\n'
                                        f'Right now, both are divisible by {gcd(self.twists, self.turns)}.\n'
-                                       f'Valid twist counts for n={self.turns} turns are: {list(divisors(self.turns, max(self.turns, 25)))}'
+                                       f'Valid twist counts for n={self.turns} turns are: {list(divisors(self.turns, max(self.turns, 25)))}\n'
                                        f'Valid turn counts for k={self.twists} twists are: {list(divisors(self.twists, max(self.twists, 25)))}')
 
         if (self.stagger_inner_vias or self.stagger_outer_vias) and self.twists%2 != 0: