| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 1 |
| 4 | 4 |
| 5 | 13 |
| 6 | 40 |
| 7 | 131 |
| 8 | 424 |
| 9 | 1428 |
| 10 | 4848 |
| 11 | 16795 |
| 12 | 58740 |
| 13 | 208011 |
| 14 | 742768 |
| 15 | 2674425 |
| 16 | 9694416 |
| 17 | 35357669 |
| 18 | 129643320 |
| 19 | 477638699 |
| 20 | 1767258324 |
| 21 | 6564120287 |
| 22 | 24466250224 |
| 23 | 91482563639 |
| 24 | 343059554440 |
| 25 | 1289904147310 |
| 26 | 4861946193440 |
| 27 | 18367353070722 |
| 28 | 69533550173100 |
| 29 | 263747951750359 |
[1,0,1,4,13,40,131,424,1428,4848,16795,58740, 208011,742768,2674425,9694416,35357669,129643320, 477638699,1767258324,6564120287,24466250224, 91482563639,343059554440,1289904147310, 4861946193440,18367353070722,69533550173100, 263747951750359] |