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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 13 |
| 5 | 50 |
| 6 | 270 |
| 7 | 1641 |
| 8 | 11945 |
| 9 | 96784 |
| 10 | 887982 |
| 11 | 8939051 |
| 12 | 99298354 |
| 13 | 1195617443 |
| 14 | 15619182139 |
| 15 | 219049941201 |
| 16 | 3293800835940 |
| 17 | 52746930894774 |
| 18 | 897802366250126 |
| 19 | 16167544246362567 |
| 20 | 307372573011579188 |
| 21 | 6148811682561390279 |
| 22 | 129164845357784003661 |
[1,1,2,4,13,50,270,1641,11945,96784,887982, 8939051,99298354,1195617443,15619182139, 219049941201,3293800835940,52746930894774, 897802366250126,16167544246362567, 307372573011579188,6148811682561390279, 129164845357784003661] |