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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 18 |
| 5 | 61 |
| 6 | 223 |
| 7 | 835 |
| 8 | 3296 |
| 9 | 13280 |
| 10 | 54828 |
| 11 | 230937 |
| 12 | 986261 |
| 13 | 4275360 |
| 14 | 18729877 |
| 15 | 82912159 |
| 16 | 370207793 |
| 17 | 1665674199 |
| 18 | 7546473001 |
| 19 | 34395212088 |
| 20 | 157636435318 |
| 21 | 725993948563 |
| 22 | 3358579055113 |
| 23 | 15600331684473 |
| 24 | 72730708595232 |
| 25 | 340230220394416 |
| 26 | 1596525730756138 |
| 27 | 7513179574478844 |
| 28 | 35450185529339379 |
[1,1,2,6,18,61,223,835,3296,13280,54828,230937, 986261,4275360,18729877,82912159,370207793, 1665674199,7546473001,34395212088,157636435318, 725993948563,3358579055113,15600331684473, 72730708595232,340230220394416,1596525730756138, 7513179574478844,35450185529339379] |