91 is the next number.
The hint is Latin for “three letters”. This is the series of Roman Numerals consisting of three symbols.
3 – III
7 – VII
12 – XII
14 – XIV
16 – XVI
19 – XIX
21 – XXI
25 – XXV
30 – XXX
41 – XLI
45 – XLV
52 – LII
54 – LIV
56 – LVI
59 – LIX
61 – LXI
65 – LXV
70 – LXX
91 – XCI