n | a(n) |
---|---|
0 | 1 |
1 | 4 |
2 | 6 |
3 | 20 |
4 | 60 |
5 | 204 |
6 | 670 |
7 | 2340 |
8 | 8160 |
9 | 29120 |
10 | 104754 |
11 | 381300 |
12 | 1397740 |
13 | 5162220 |
14 | 19172790 |
15 | 71582716 |
16 | 268431360 |
17 | 1010580540 |
18 | 3817733920 |
19 | 14467258260 |
20 | 54975528948 |
21 | 209430785460 |
22 | 799644629550 |
23 | 3059510616420 |
[1,4,6,20,60,204,670,2340,8160,29120,104754, 381300,1397740,5162220,19172790,71582716, 268431360,1010580540,3817733920,14467258260, 54975528948,209430785460,799644629550, 3059510616420] |