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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 8 |
| 4 | 18 |
| 5 | 40 |
| 6 | 92 |
| 7 | 208 |
| 8 | 470 |
| 9 | 1060 |
| 10 | 2384 |
| 11 | 5352 |
| 12 | 11992 |
| 13 | 26824 |
| 14 | 59906 |
| 15 | 133592 |
| 16 | 297510 |
| 17 | 661720 |
| 18 | 1470062 |
| 19 | 3262264 |
| 20 | 7231940 |
| 21 | 16016596 |
| 22 | 35439722 |
| 23 | 78349800 |
| 24 | 173074816 |
| 25 | 382029988 |
| 26 | 842648168 |
| 27 | 1857362384 |
| 28 | 4091321478 |
| 29 | 9006604780 |
| 30 | 19815365450 |
[0,4,8,18,40,92,208,470,1060,2384,5352,11992, 26824,59906,133592,297510,661720,1470062,3262264, 7231940,16016596,35439722,78349800,173074816, 382029988,842648168,1857362384,4091321478, 9006604780,19815365450] |