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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 15 |
| 5 | 45 |
| 6 | 135 |
| 7 | 422 |
| 8 | 1357 |
| 9 | 4503 |
| 10 | 15301 |
| 11 | 53225 |
| 12 | 189070 |
| 13 | 684540 |
| 14 | 2522194 |
| 15 | 9441960 |
| 16 | 35867225 |
| 17 | 138080428 |
| 18 | 538155330 |
| 19 | 2121211604 |
| 20 | 8448577175 |
| 21 | 33974559322 |
| 22 | 137842934746 |
| 23 | 563885092371 |
| 24 | 2324435490519 |
| 25 | 9650120731330 |
| 26 | 40329864236526 |
| 27 | 169593208033062 |
[1,1,2,6,15,45,135,422,1357,4503,15301,53225, 189070,684540,2522194,9441960,35867225,138080428, 538155330,2121211604,8448577175,33974559322, 137842934746,563885092371,2324435490519, 9650120731330,40329864236526,169593208033062] |