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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 8 |
| 3 | 33 |
| 4 | 124 |
| 5 | 644 |
| 6 | 3288 |
| 7 | 18883 |
| 8 | 108284 |
| 9 | 642234 |
| 10 | 3808768 |
| 11 | 22785833 |
| 12 | 136315044 |
| 13 | 817291024 |
| 14 | 4900153448 |
| 15 | 29395534383 |
| 16 | 176340899404 |
| 17 | 1057996947014 |
| 18 | 6347691029328 |
| 19 | 38085710240533 |
| 20 | 228511646005364 |
| 21 | 1371065953050204 |
[1,4,8,33,124,644,3288,18883,108284,642234, 3808768,22785833,136315044,817291024,4900153448, 29395534383,176340899404,1057996947014, 6347691029328,38085710240533,228511646005364, 1371065953050204] |