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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 42 |
| 3 | 308 |
| 4 | 2310 |
| 5 | 17556 |
| 6 | 134596 |
| 7 | 1038312 |
| 8 | 8046918 |
| 9 | 62587140 |
| 10 | 488179692 |
| 11 | 3816677592 |
| 12 | 29897307804 |
| 13 | 234578876616 |
| 14 | 1843119744840 |
| 15 | 14499208659408 |
| 16 | 114181268192838 |
| 17 | 900017055167076 |
| 18 | 7100134546318044 |
| 19 | 56053693786721400 |
| 20 | 442824180915099060 |
| 21 | 3500419715805068760 |
| 22 | 27685137752276452920 |
[1,6,42,308,2310,17556,134596,1038312,8046918, 62587140,488179692,3816677592,29897307804, 234578876616,1843119744840,14499208659408, 114181268192838,900017055167076,7100134546318044, 56053693786721400,442824180915099060, 3500419715805068760,27685137752276452920] |