diff --git a/benchmark/benchmarking.py b/benchmark/benchmarking.py
index 68a2433..08b37ef 100644
--- a/benchmark/benchmarking.py
+++ b/benchmark/benchmarking.py
@@ -324,12 +324,13 @@ def update(self):
 
     def auto_number(self) -> int:
         assert self.is_auto_number
-        for expo in itertools.count(3):
-            for n in (1, 2, 5):
-                self.number = n * 10**expo
-                runtime = self.run().runtime
+        for self.number in auto_number_series():
+            with temp_log():
+                log(numerize(self.number, decimals=1), False)
+                runtime = min(self.run().runtime for _ in range(5))
                 if runtime > AUTO_NUMBER_TARGET_TIME:
                     return runtime
+                self.number = int(self.number * 1.1)
 
     def run(self) -> "TestCaseResult":
         log(".", False)
diff --git a/benchmark/utils.py b/benchmark/utils.py
index 110c501..a3cc43c 100644
--- a/benchmark/utils.py
+++ b/benchmark/utils.py
@@ -31,11 +31,18 @@
     "log",
     "indent_log",
     "temp_log",
-    "iter_identity"
+    "iter_identity",
+    "auto_number_series"
 )
 
 SourceLines = Tuple[str, ...]
 
+def auto_number_series() -> Generator[int, None, None]:
+    for expo in itertools.count(2):
+        # E12 series
+        for value in (10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82):
+            yield value * 10 ** expo
+
 def indent(src: SourceLines) -> SourceLines:
     return tuple(" "*4 + line for line in src)