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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 66 |
| 4 | 280 |
| 5 | 1218 |
| 6 | 5422 |
| 7 | 24666 |
| 8 | 114540 |
| 9 | 542278 |
| 10 | 2614178 |
| 11 | 12814102 |
| 12 | 63772982 |
| 13 | 321754290 |
| 14 | 1643263134 |
| 15 | 8483485886 |
| 16 | 44214343344 |
| 17 | 232362906298 |
| 18 | 1230090777342 |
| 19 | 6553657204178 |
| 20 | 35113127086114 |
| 21 | 189062666857686 |
| 22 | 1022459506515674 |
[1,4,16,66,280,1218,5422,24666,114540,542278, 2614178,12814102,63772982,321754290,1643263134, 8483485886,44214343344,232362906298,1230090777342, 6553657204178,35113127086114,189062666857686, 1022459506515674] |