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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 18 |
| 5 | 45 |
| 6 | 102 |
| 7 | 213 |
| 8 | 426 |
| 9 | 821 |
| 10 | 1538 |
| 11 | 2820 |
| 12 | 5075 |
| 13 | 8996 |
| 14 | 15743 |
| 15 | 27247 |
| 16 | 46709 |
| 17 | 79405 |
| 18 | 133996 |
| 19 | 224640 |
| 20 | 374400 |
[0,1,2,6,18,45,102,213,426,821,1538,2820,5075, 8996,15743,27247,46709,79405,133996,224640,374400] |