Primitive elvish
lepen
root. five
lepe
noun. finger
lepene
noun. five
lepenya
ordinal. 5th
lepem
root. five
leper
noun. finger
lepero
noun. finger
lenep
root. five
lepen
root. five
lepe
noun. finger
lepene
noun. five
lepenya
ordinal. 5th
lepem
root. five
leper
noun. finger
lepero
noun. finger
lenep
root. five
√LEPEN was the most common root for “five” in Tolkien’s writings, but he explored a variety of other options. Its earliest iteration appeared in the Qenya and Gnomish lexicons as ᴱ√LEH (QL/52) or ᴱ√LEF “half” (GL/53), so I think the actual early form was ✱ᴱ√LEǶE [lexʷe]. At this early stage it had derivatives with the meanings “five”, “ten”, and “half”, but in later writings “ten” became ᴹ√KAYAN >> √KWAY(AM) and “half” became √PER.
In The Etymologies of the 1930s the root appeared as ᴹ√LEPEN “five” with variant ᴹ√LEPEK, but ᴹ√LEPEK had no derivatives (Ety/LEP). √LEPEN appeared again in a list of numbers from the late 1950s or early 1960s beside a variant √LENEP; again the variant had no clear derivatives (PE17/95). √LEPEN reappeared in numeric discussions from the late 1960s (VT42/24; VT47/10). In these late discussions Tolkien said that “five” most likely originally from ✱lepem as an ancient plural of √LEP, but it seems this became √LEPEN already in Common Eldarin (CE), given that the Sindarin word for “five” remained S. leben; Tolkien gave varying explanations for this CE sound change, either as dissimilation from p (VT47/26 note 2) or with final -m > -n being the regular phonetic development (VT47/24).