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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 1 |
| 4 | 4 |
| 5 | 4 |
| 6 | 16 |
| 7 | 22 |
| 8 | 70 |
| 9 | 132 |
| 10 | 375 |
| 11 | 848 |
| 12 | 2428 |
| 13 | 6256 |
| 14 | 18333 |
| 15 | 52560 |
| 16 | 161436 |
| 17 | 500887 |
| 18 | 1624969 |
| 19 | 5384625 |
| 20 | 18438815 |
| 21 | 64674095 |
| 22 | 233062429 |
| 23 | 859831186 |
| 24 | 3248411250 |
| 25 | 12545820860 |
| 26 | 49508089411 |
| 27 | 199410275018 |
| 28 | 819269777688 |
| 29 | 3430680180687 |
| 30 | 14633035575435 |
| 31 | 63535672197070 |
[1,0,1,1,4,4,16,22,70,132,375,848,2428,6256,18333, 52560,161436,500887,1624969,5384625,18438815, 64674095,233062429,859831186,3248411250, 12545820860,49508089411,199410275018,819269777688, 3430680180687,14633035575435,63535672197070] |