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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 3 |
| 5 | 3 |
| 6 | 4 |
| 7 | 18 |
| 8 | 45 |
| 9 | 72 |
| 10 | 153 |
| 11 | 450 |
| 12 | 1066 |
| 13 | 2172 |
| 14 | 5142 |
| 15 | 13381 |
| 16 | 31752 |
| 17 | 72333 |
| 18 | 176475 |
| 19 | 441909 |
| 20 | 1065528 |
| 21 | 2551465 |
| 22 | 6292857 |
| 23 | 15620439 |
| 24 | 38229235 |
| 25 | 93698523 |
| 26 | 232545105 |
| 27 | 578019090 |
| 28 | 1430290512 |
| 29 | 3548336724 |
| 30 | 8851036863 |
| 31 | 22092054588 |
| 32 | 55093739760 |
| 33 | 137681640450 |
[1,0,0,1,3,3,4,18,45,72,153,450,1066,2172,5142, 13381,31752,72333,176475,441909,1065528,2551465, 6292857,15620439,38229235,93698523,232545105, 578019090,1430290512,3548336724,8851036863, 22092054588,55093739760,137681640450] |