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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 18 |
| 5 | 52 |
| 6 | 148 |
| 7 | 420 |
| 8 | 1192 |
| 9 | 3384 |
| 10 | 9608 |
| 11 | 27280 |
| 12 | 77456 |
| 13 | 219920 |
| 14 | 624416 |
| 15 | 1772896 |
| 16 | 5033760 |
| 17 | 14292288 |
| 18 | 40579904 |
| 19 | 115217984 |
| 20 | 327136896 |
| 21 | 928835456 |
| 22 | 2637230208 |
| 23 | 7487852800 |
| 24 | 21260161280 |
| 25 | 60363694336 |
| 26 | 171389837824 |
| 27 | 486624896512 |
| 28 | 1381667623424 |
| 29 | 3922950583296 |
[0,1,2,6,18,52,148,420,1192,3384,9608,27280,77456, 219920,624416,1772896,5033760,14292288,40579904, 115217984,327136896,928835456,2637230208, 7487852800,21260161280,60363694336,171389837824, 486624896512,1381667623424,3922950583296] |