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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 12 |
| 3 | 56 |
| 4 | 228 |
| 5 | 920 |
| 6 | 3684 |
| 7 | 14744 |
| 8 | 58980 |
| 9 | 235928 |
| 10 | 943716 |
| 11 | 3774872 |
| 12 | 15099492 |
| 13 | 60397976 |
| 14 | 241591908 |
| 15 | 966367640 |
| 16 | 3865470564 |
| 17 | 15461882264 |
| 18 | 61847529060 |
| 19 | 247390116248 |
| 20 | 989560464996 |
| 21 | 3958241859992 |
| 22 | 15832967439972 |
[0,2,12,56,228,920,3684,14744,58980,235928,943716, 3774872,15099492,60397976,241591908,966367640, 3865470564,15461882264,61847529060,247390116248, 989560464996,3958241859992,15832967439972] |