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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 6 |
| 3 | 22 |
| 4 | 182 |
| 5 | 490 |
| 6 | 3510 |
| 7 | 9240 |
| 8 | 63868 |
| 9 | 1149468 |
| 10 | 3009672 |
| 11 | 54017304 |
| 12 | 370246314 |
| 13 | 969319296 |
| 14 | 6643832358 |
| 15 | 119218840092 |
| 16 | 2139295466336 |
| 17 | 5600748260454 |
| 18 | 100501350226466 |
| 19 | 688846502491240 |
| 20 | 1803423556642478 |
| 21 | 32361122671978600 |
| 22 | 221806434537503870 |
| 23 | 3980154972736116440 |
[0,2,6,22,182,490,3510,9240,63868,1149468,3009672, 54017304,370246314,969319296,6643832358, 119218840092,2139295466336,5600748260454, 100501350226466,688846502491240,1803423556642478, 32361122671978600,221806434537503870, 3980154972736116440] |