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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 4 |
| 6 | 11 |
| 7 | 28 |
| 8 | 87 |
| 9 | 266 |
| 10 | 952 |
| 11 | 3381 |
| 12 | 13513 |
| 13 | 53915 |
| 14 | 237113 |
| 15 | 1046732 |
| 16 | 5016728 |
| 17 | 24186664 |
| 18 | 125121009 |
| 19 | 652084528 |
| 20 | 3615047527 |
| 21 | 20211789423 |
| 22 | 119384499720 |
| 23 | 711572380960 |
| 24 | 4455637803543 |
| 25 | 28162688795697 |
| 26 | 186152008588691 |
| 27 | 1242276416218540 |
| 28 | 8636436319397292 |
[1,0,1,1,2,4,11,28,87,266,952,3381,13513,53915, 237113,1046732,5016728,24186664,125121009, 652084528,3615047527,20211789423,119384499720, 711572380960,4455637803543,28162688795697, 186152008588691,1242276416218540,8636436319397292] |