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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 15 |
| 3 | 57 |
| 4 | 219 |
| 5 | 848 |
| 6 | 3302 |
| 7 | 12911 |
| 8 | 50643 |
| 9 | 199140 |
| 10 | 784626 |
| 11 | 3096514 |
| 12 | 12236830 |
| 13 | 48412432 |
| 14 | 191718188 |
| 15 | 759852347 |
| 16 | 3013746563 |
| 17 | 11960699132 |
| 18 | 47494802618 |
| 19 | 188689585982 |
| 20 | 749961486698 |
| 21 | 2981943800192 |
| 22 | 11860758904148 |
| 23 | 47191458566582 |
[1,4,15,57,219,848,3302,12911,50643,199140,784626, 3096514,12236830,48412432,191718188,759852347, 3013746563,11960699132,47494802618,188689585982, 749961486698,2981943800192,11860758904148, 47191458566582] |