n | a(n) |
---|---|
1 | 1 |
2 | 4 |
3 | 20 |
4 | 90 |
5 | 420 |
6 | 1910 |
7 | 8820 |
8 | 40590 |
9 | 187880 |
10 | 871494 |
11 | 4057620 |
12 | 18945960 |
13 | 88738020 |
14 | 416787030 |
15 | 1962922276 |
16 | 9268287390 |
17 | 43868210820 |
18 | 208109782580 |
19 | 989400443220 |
20 | 4713395564772 |
21 | 22497100553820 |
22 | 107572434560790 |
23 | 515241748300020 |
[1,4,20,90,420,1910,8820,40590,187880,871494, 4057620,18945960,88738020,416787030,1962922276, 9268287390,43868210820,208109782580,989400443220, 4713395564772,22497100553820,107572434560790, 515241748300020] |