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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 30 |
| 3 | 150 |
| 4 | 738 |
| 5 | 3570 |
| 6 | 17118 |
| 7 | 81498 |
| 8 | 385710 |
| 9 | 1817046 |
| 10 | 8528478 |
| 11 | 39903462 |
| 12 | 186198642 |
| 13 | 866861394 |
| 14 | 4027766490 |
| 15 | 18681900270 |
| 16 | 86518735722 |
| 17 | 400136695074 |
| 18 | 1848320799438 |
| 19 | 8528448008214 |
[1,6,30,150,738,3570,17118,81498,385710,1817046, 8528478,39903462,186198642,866861394,4027766490, 18681900270,86518735722,400136695074, 1848320799438,8528448008214] |