Primitive elvish
lepe
noun. finger
lepethron
noun. lepethron
lepen
root. five
lepene
noun. five
lepenya
ordinal. 5th
leper
noun. finger
lepero
noun. finger
lepetā
noun. thumb, ‘picker’; finger
lepem
root. five
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).