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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 22 |
| 6 | 71 |
| 7 | 240 |
| 8 | 816 |
| 9 | 2752 |
| 10 | 9313 |
| 11 | 31514 |
| 12 | 106590 |
| 13 | 360606 |
| 14 | 1219935 |
| 15 | 4126960 |
| 16 | 13961456 |
| 17 | 47231280 |
| 18 | 159782161 |
| 19 | 540539330 |
| 20 | 1828631430 |
| 21 | 6186215574 |
| 22 | 20927817799 |
| 23 | 70798300288 |
| 24 | 239508933824 |
| 25 | 810252920400 |
| 26 | 2741065994769 |
| 27 | 9272959837818 |
| 28 | 31370198430718 |
[0,0,1,2,6,22,71,240,816,2752,9313,31514,106590, 360606,1219935,4126960,13961456,47231280, 159782161,540539330,1828631430,6186215574, 20927817799,70798300288,239508933824,810252920400, 2741065994769,9272959837818,31370198430718] |