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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 45 |
| 5 | 174 |
| 6 | 693 |
| 7 | 2891 |
| 8 | 12156 |
| 9 | 52538 |
| 10 | 228973 |
| 11 | 1012996 |
| 12 | 4518961 |
| 13 | 20342820 |
| 14 | 92221108 |
| 15 | 420719274 |
| 16 | 1930067929 |
| 17 | 8897118329 |
| 18 | 41194214136 |
| 19 | 191470957420 |
| 20 | 893110958485 |
| 21 | 4179139628301 |
| 22 | 19612391986898 |
| 23 | 92283693683299 |
| 24 | 435288156265051 |
| 25 | 2057796624112995 |
| 26 | 9748277239594671 |
| 27 | 46268733559268079 |
[1,1,4,12,45,174,693,2891,12156,52538,228973, 1012996,4518961,20342820,92221108,420719274, 1930067929,8897118329,41194214136,191470957420, 893110958485,4179139628301,19612391986898, 92283693683299,435288156265051,2057796624112995, 9748277239594671,46268733559268079] |