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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 10 |
| 4 | 21 |
| 5 | 72 |
| 6 | 330 |
| 7 | 468 |
| 8 | 2520 |
| 9 | 8160 |
| 10 | 20520 |
| 11 | 60480 |
| 12 | 318780 |
| 13 | 504000 |
| 14 | 2426112 |
| 15 | 10523520 |
| 16 | 21092400 |
| 17 | 53222400 |
| 18 | 452390400 |
| 19 | 506373120 |
| 20 | 3226728960 |
| 21 | 11604902400 |
| 22 | 21299241600 |
| 23 | 76640256000 |
| 24 | 431500608000 |
| 25 | 844958822400 |
| 26 | 3197988864000 |
| 27 | 10492449177600 |
| 28 | 38109367296000 |
[1,1,3,10,21,72,330,468,2520,8160,20520,60480, 318780,504000,2426112,10523520,21092400,53222400, 452390400,506373120,3226728960,11604902400, 21299241600,76640256000,431500608000,844958822400, 3197988864000,10492449177600,38109367296000] |