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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 5 |
| 5 | 18 |
| 6 | 84 |
| 7 | 481 |
| 8 | 3249 |
| 9 | 25359 |
| 10 | 224000 |
| 11 | 2208441 |
| 12 | 24019991 |
| 13 | 285633470 |
| 14 | 3685413373 |
| 15 | 51271476627 |
| 16 | 764944009086 |
| 17 | 12182390286127 |
| 18 | 206262410584138 |
| 19 | 3699483818281188 |
| 20 | 70067511789111404 |
| 21 | 1397379232420943285 |
[1,1,1,2,5,18,84,481,3249,25359,224000,2208441, 24019991,285633470,3685413373,51271476627, 764944009086,12182390286127,206262410584138, 3699483818281188,70067511789111404, 1397379232420943285] |