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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 12 |
| 3 | 74 |
| 4 | 464 |
| 5 | 2997 |
| 6 | 19704 |
| 7 | 131140 |
| 8 | 880912 |
| 9 | 5960000 |
| 10 | 40555117 |
| 11 | 277251834 |
| 12 | 1902791048 |
| 13 | 13101878220 |
| 14 | 90468268336 |
| 15 | 626202992439 |
| 16 | 4343671952768 |
| 17 | 30186478566432 |
| 18 | 210131106485088 |
| 19 | 1464920605002240 |
| 20 | 10226302297174509 |
| 21 | 71474029751497258 |
| 22 | 500097817634501780 |
[1,2,12,74,464,2997,19704,131140,880912,5960000, 40555117,277251834,1902791048,13101878220, 90468268336,626202992439,4343671952768, 30186478566432,210131106485088,1464920605002240, 10226302297174509,71474029751497258, 500097817634501780] |