Numerical values of Latin letters

[Jonathan Post]

Continuing, if I'm right at all, we'd have a(1)-a(50) as

A132984 4, 3, 4, 8, 7, 3, 6, 4, 5, 5, 7, 8, 8, 13, 9, 7, 11, 12, 11,
 7, 11, 10, 11, 15, 14, 10, 13, 13, 12, 8, 12, 11, 12, 16, 15, 11, 14,
 16, 15, 11, 15, 14, 15, 19, 18, 14, 17, 16, 12

with 40 through 50 being:

quadraginta, quadraginta unus, quadraginta duo, quadraginta tres,
quadraginta quattuor, quadraginta quinque, quadraginta sex,
quadraginta septem, duodequinquaginta, undequinquagginta, quinquaginta

Now we have the makings of the inverse function:

Least cardinal integer which has exactly n letters in its Latin
name [can someone please verify and extend?]

n  a(n) namely
3   2     duo
4   1     unus
5   9     novem
6   7     septem
7   5     quinque
8   4     quattuor
9   15   quindecim
10 22   viginti duo
11 17   septemdecim
12 18   duodeviginti
13 14   quattuordecim
14 25   viginti quinque
15 24   viginti quattuor
16 34   triginta quattuor
17 47   quadraginta septem
18 45   quadraginta quinque
19 44   quadraginta quattuor
20 54   quinquaginta quattuor