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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 2 |
| 4 | 8 |
| 5 | 14 |
| 6 | 54 |
| 7 | 128 |
| 8 | 498 |
| 9 | 1426 |
| 10 | 5736 |
| 11 | 18814 |
| 12 | 78886 |
| 13 | 287296 |
| 14 | 1258018 |
| 15 | 4986402 |
| 16 | 22789000 |
| 17 | 96966318 |
| 18 | 461790998 |
| 19 | 2088374592 |
| 20 | 10343408786 |
| 21 | 49343711666 |
| 22 | 253644381032 |
| 23 | 1268995609502 |
| 24 | 6756470362374 |
| 25 | 35285321738624 |
| 26 | 194220286045506 |
| 27 | 1054759508543554 |
[1,0,2,2,8,14,54,128,498,1426,5736,18814,78886, 287296,1258018,4986402,22789000,96966318, 461790998,2088374592,10343408786,49343711666, 253644381032,1268995609502,6756470362374, 35285321738624,194220286045506,1054759508543554] |