FWIW, here are a few numbers. Most of them are new, and I didn't bother to sort out the existing ones. Earlier references for 34 and 36 weren't correct, unfortunately.
By feeding all the numbers into a spreadsheet graph, I discovered these special features:
I'll call the difference from level to level "steps" and the increase in value of the steps "gradient".
First stage for beginners is up to lvl 25 (5290 XPs), with a small gradient in the steps (505 to lvl 25). From 27 till 75, steps grow by 100 per level, starting from 1000 to 5700 (the gradient is constantly 100 per step: 1100, 1200, 1300...). Here, all levels start with 15 as the last digits, 140215 for lvl 75.
Furtheron, the gradients of the steps stay below 5000 until level 90. From there on the steps increase quickly, until 220.000 towards lvl 97.
Here the numbers from lvl 14 to 76 (77 to 97 have been posted here already):
Lvl min.XPs
14 1310
15 1540
16 1795
17 2075
18 2380
19 2710
20 3065
21 3450
22 3865
23 4310
24 4785
25 5290
26 6040
27 6915
28 7915
29 9015
30 10215
31 11515
32 12915
33 14415
34 16015
35 17715
36 19515
37 21415
38 23415
39 25515
40 27715
41 30015
42 32415
43 34915
44 37515
45 40215
46 43015
47 45915
48 48915
49 52015
50 55215
51 58515
52 61915
53 65415
54 69015
55 72715
56 76515
57 80415
58 84415
59 88515
60 92715
61 97015
62 101415
63 105915
64 110515
65 115215
66 120015
67 124915
68 129915
69 135015
70 140215
71 145515
72 150915
73 156415
74 162015
75 167715
76 173915