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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 18 |
| 5 | 61 |
| 6 | 281 |
| 7 | 1541 |
| 8 | 8920 |
| 9 | 57924 |
| 10 | 437490 |
| 11 | 3611389 |
| 12 | 31721537 |
| 13 | 304085783 |
| 14 | 3180772870 |
| 15 | 35422074330 |
| 16 | 418050879810 |
| 17 | 5266547286061 |
| 18 | 70459362412265 |
| 19 | 991921937012273 |
| 20 | 14681437097585260 |
| 21 | 228615478225446360 |
| 22 | 3730868960721027906 |
| 23 | 63577641238069645741 |
[1,1,2,6,18,61,281,1541,8920,57924,437490,3611389, 31721537,304085783,3180772870,35422074330, 418050879810,5266547286061,70459362412265, 991921937012273,14681437097585260, 228615478225446360,3730868960721027906, 63577641238069645741] |