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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 16 |
| 3 | 64 |
| 4 | 252 |
| 5 | 984 |
| 6 | 3816 |
| 7 | 14724 |
| 8 | 56592 |
| 9 | 216864 |
| 10 | 829116 |
| 11 | 3164184 |
| 12 | 12058632 |
| 13 | 45904644 |
| 14 | 174598416 |
| 15 | 663634944 |
| 16 | 2521077372 |
| 17 | 9573268824 |
| 18 | 36340434216 |
| 19 | 137913296004 |
| 20 | 523277751312 |
| 21 | 1985122823904 |
| 22 | 7529850771516 |
| 23 | 28558867923864 |
[4,16,64,252,984,3816,14724,56592,216864,829116, 3164184,12058632,45904644,174598416,663634944, 2521077372,9573268824,36340434216,137913296004, 523277751312,1985122823904,7529850771516, 28558867923864] |