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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 10 |
| 3 | 52 |
| 4 | 290 |
| 5 | 1706 |
| 6 | 10440 |
| 7 | 65822 |
| 8 | 424710 |
| 9 | 2791340 |
| 10 | 18622510 |
| 11 | 125791894 |
| 12 | 858621680 |
| 13 | 5913143706 |
| 14 | 41036613570 |
| 15 | 286702877908 |
| 16 | 2014876764170 |
| 17 | 14234073943986 |
| 18 | 101025202379480 |
| 19 | 720017430722598 |
| 20 | 5151008515543790 |
[1,2,10,52,290,1706,10440,65822,424710,2791340, 18622510,125791894,858621680,5913143706, 41036613570,286702877908,2014876764170, 14234073943986,101025202379480,720017430722598, 5151008515543790] |