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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 4 |
| 4 | 15 |
| 5 | 15 |
| 6 | 56 |
| 7 | 56 |
| 8 | 210 |
| 9 | 210 |
| 10 | 792 |
| 11 | 792 |
| 12 | 3003 |
| 13 | 3003 |
| 14 | 11440 |
| 15 | 11440 |
| 16 | 43758 |
| 17 | 43758 |
| 18 | 167960 |
| 19 | 167960 |
| 20 | 646646 |
| 21 | 646646 |
| 22 | 2496144 |
| 23 | 2496144 |
| 24 | 9657700 |
| 25 | 9657700 |
| 26 | 37442160 |
| 27 | 37442160 |
| 28 | 145422675 |
| 29 | 145422675 |
| 30 | 565722720 |
[1,1,4,4,15,15,56,56,210,210,792,792,3003,3003, 11440,11440,43758,43758,167960,167960,646646, 646646,2496144,2496144,9657700,9657700,37442160, 37442160,145422675,145422675,565722720] |