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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 7 |
| 4 | 16 |
| 5 | 46 |
| 6 | 110 |
| 7 | 295 |
| 8 | 720 |
| 9 | 1870 |
| 10 | 4612 |
| 11 | 11782 |
| 12 | 29224 |
| 13 | 73984 |
| 14 | 184102 |
| 15 | 463687 |
| 16 | 1156000 |
| 17 | 2902870 |
| 18 | 7245020 |
| 19 | 18161170 |
| 20 | 45356736 |
| 21 | 113576596 |
| 22 | 283765132 |
| 23 | 710118262 |
| 24 | 1774619616 |
| 25 | 4439253196 |
| 26 | 11095532840 |
| 27 | 27749232700 |
| 28 | 69363052600 |
[0,1,2,7,16,46,110,295,720,1870,4612,11782,29224, 73984,184102,463687,1156000,2902870,7245020, 18161170,45356736,113576596,283765132,710118262, 1774619616,4439253196,11095532840,27749232700, 69363052600] |