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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 8 |
| 4 | 31 |
| 5 | 130 |
| 6 | 590 |
| 7 | 2798 |
| 8 | 13541 |
| 9 | 66724 |
| 10 | 332708 |
| 11 | 1673536 |
| 12 | 8479367 |
| 13 | 43218034 |
| 14 | 221383712 |
| 15 | 1138976166 |
| 16 | 5882112985 |
| 17 | 30479772624 |
| 18 | 158413903096 |
| 19 | 825556260636 |
| 20 | 4312814257059 |
| 21 | 22580855859166 |
| 22 | 118468635595680 |
| 23 | 622698941708890 |
[1,0,2,8,31,130,590,2798,13541,66724,332708, 1673536,8479367,43218034,221383712,1138976166, 5882112985,30479772624,158413903096,825556260636, 4312814257059,22580855859166,118468635595680, 622698941708890] |