diff --git a/utm/conversion.py b/utm/conversion.py
old mode 100755
new mode 100644
index d21742a..449f3d1
--- a/utm/conversion.py
+++ b/utm/conversion.py
@@ -216,13 +216,13 @@ def latlon_to_zone_number(latitude, longitude):
         return 32
 
     if 72 <= latitude <= 84 and longitude >= 0:
-        if longitude <= 9:
+        if longitude < 9:
             return 31
-        elif longitude <= 21:
+        elif longitude < 21:
             return 33
-        elif longitude <= 33:
+        elif longitude < 33:
             return 35
-        elif longitude <= 42:
+        elif longitude < 42:
             return 37
 
     return int((longitude + 180) / 6) + 1

UTM zone exceptions error
By definition zones are left-closed, right-open intervals, e.g. zone 31: 0 <= latitude < 6.
In function latlon_to_zone_number:

```
if 72 <= latitude <= 84 and longitude >= 0:
    if longitude <= 9:
        return 31
    elif longitude <= 21:
        return 33
    elif longitude <= 33:
        return 35
    elif longitude <= 42:
        return 37
```

For latitudes >=72, this results in:
zone 31: 0  <= longitude <= 9
zone 33: 9  <   longitude <= 21
zone 35: 21<   longitude <= 33
zone 37: 33<   longitude <= 42

but for latitudes < 72:
zone 37: 36 <= latitude < 42

diff --git a/test/test_utm.py b/test/test_utm.py
index 55686d7..c820cea 100755
--- a/test/test_utm.py
+++ b/test/test_utm.py
@@ -231,5 +231,22 @@ class Zone32V(unittest.TestCase):
         self.assert_zone_equal(UTM.from_latlon(64, 12), 33, 'W')
 
 
+class TestRightBoundaries(unittest.TestCase):
+
+    def assert_zone_equal(self, result, expected_number):
+        self.assertEqual(result[2], expected_number)
+
+    def test_limits(self):
+        self.assert_zone_equal(UTM.from_latlon(40, 0), 31)
+        self.assert_zone_equal(UTM.from_latlon(40, 5.999999), 31)
+        self.assert_zone_equal(UTM.from_latlon(40, 6), 32)
+
+        self.assert_zone_equal(UTM.from_latlon(72, 0), 31)
+        self.assert_zone_equal(UTM.from_latlon(72, 5.999999), 31)
+        self.assert_zone_equal(UTM.from_latlon(72, 6), 31)
+        self.assert_zone_equal(UTM.from_latlon(72, 8.999999), 31)
+        self.assert_zone_equal(UTM.from_latlon(72, 9), 33)
+
+
 if __name__ == '__main__':
     unittest.main()

pip install -e .
parse_log_pytest
pytest
pytest
3.5
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
attrs @ file:///opt/conda/conda-bld/attrs_1642510447205/work
certifi==2021.5.30
importlib-metadata @ file:///tmp/build/80754af9/importlib-metadata_1631916693255/work
iniconfig @ file:///home/linux1/recipes/ci/iniconfig_1610983019677/work
more-itertools @ file:///tmp/build/80754af9/more-itertools_1637733554872/work
packaging @ file:///tmp/build/80754af9/packaging_1637314298585/work
pluggy @ file:///tmp/build/80754af9/pluggy_1615976315926/work
py @ file:///opt/conda/conda-bld/py_1644396412707/work
pyparsing @ file:///tmp/build/80754af9/pyparsing_1635766073266/work
pytest==6.2.4
toml @ file:///tmp/build/80754af9/toml_1616166611790/work
typing_extensions @ file:///opt/conda/conda-bld/typing_extensions_1647553014482/work
-e git+https://github.com/Turbo87/utm.git@4c7c13f2b2b9c01a8581392641aeb8bbda6aba6f#egg=utm
zipp @ file:///tmp/build/80754af9/zipp_1633618647012/work

name: utm
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - attrs=21.4.0=pyhd3eb1b0_0
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - importlib-metadata=4.8.1=py36h06a4308_0
  - importlib_metadata=4.8.1=hd3eb1b0_0
  - iniconfig=1.1.1=pyhd3eb1b0_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - more-itertools=8.12.0=pyhd3eb1b0_0
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - packaging=21.3=pyhd3eb1b0_0
  - pip=21.2.2=py36h06a4308_0
  - pluggy=0.13.1=py36h06a4308_0
  - py=1.11.0=pyhd3eb1b0_0
  - pyparsing=3.0.4=pyhd3eb1b0_0
  - pytest=6.2.4=py36h06a4308_2
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - setuptools=58.0.4=py36h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - toml=0.10.2=pyhd3eb1b0_0
  - typing_extensions=4.1.1=pyh06a4308_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zipp=3.6.0=pyhd3eb1b0_0
  - zlib=1.2.13=h5eee18b_1
prefix: /opt/conda/envs/utm

test/test_utm.py::TestRightBoundaries::test_limits
test/test_utm.py::KnownValues::test_from_latlon test/test_utm.py::KnownValues::test_to_latlon test/test_utm.py::BadInput::test_from_latlon_range_checks test/test_utm.py::BadInput::test_to_latlon_range_checks test/test_utm.py::Zone32V::test_above test/test_utm.py::Zone32V::test_below test/test_utm.py::Zone32V::test_inside test/test_utm.py::Zone32V::test_left_of test/test_utm.py::Zone32V::test_right_of
utm/conversion.py
utm/conversion.py