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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 16 |
| 3 | 60 |
| 4 | 222 |
| 5 | 804 |
| 6 | 2872 |
| 7 | 10132 |
| 8 | 35383 |
| 9 | 122480 |
| 10 | 420752 |
| 11 | 1435736 |
| 12 | 4870132 |
| 13 | 16432216 |
| 14 | 55178416 |
| 15 | 184481816 |
| 16 | 614348813 |
| 17 | 2038435340 |
| 18 | 6740997616 |
| 19 | 22223182372 |
| 20 | 73053304378 |
| 21 | 239502956924 |
| 22 | 783241953896 |
| 23 | 2555428926860 |
| 24 | 8319101465587 |
[4,16,60,222,804,2872,10132,35383,122480,420752, 1435736,4870132,16432216,55178416,184481816, 614348813,2038435340,6740997616,22223182372, 73053304378,239502956924,783241953896, 2555428926860,8319101465587] |