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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 12 |
| 4 | 70 |
| 5 | 426 |
| 6 | 2708 |
| 7 | 17846 |
| 8 | 121014 |
| 9 | 839388 |
| 10 | 5929162 |
| 11 | 42509318 |
| 12 | 308561388 |
| 13 | 2263197114 |
| 14 | 16748071210 |
| 15 | 124893822012 |
| 16 | 937612685502 |
| 17 | 7080464093282 |
| 18 | 53748285892004 |
| 19 | 409909445733950 |
| 20 | 3139241855256334 |
| 21 | 24132284421690988 |
[0,2,12,70,426,2708,17846,121014,839388,5929162, 42509318,308561388,2263197114,16748071210, 124893822012,937612685502,7080464093282, 53748285892004,409909445733950,3139241855256334, 24132284421690988] |