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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 4 |
| 3 | 4 |
| 4 | 28 |
| 5 | 60 |
| 6 | 264 |
| 7 | 784 |
| 8 | 3004 |
| 9 | 10204 |
| 10 | 37824 |
| 11 | 135784 |
| 12 | 502784 |
| 13 | 1851200 |
| 14 | 6901696 |
| 15 | 25766144 |
| 16 | 96797244 |
| 17 | 364655100 |
| 18 | 1379120400 |
| 19 | 5230011896 |
| 20 | 19890313128 |
| 21 | 75823622984 |
| 22 | 289698620336 |
| 23 | 1109059301536 |
| 24 | 4253731156128 |
| 25 | 16342545417760 |
| 26 | 62885474132992 |
| 27 | 242331022479040 |
| 28 | 935085717105792 |
| 29 | 3612737418620032 |
| 30 | 13974224404904704 |
[1,0,4,4,28,60,264,784,3004,10204,37824,135784, 502784,1851200,6901696,25766144,96797244, 364655100,1379120400,5230011896,19890313128, 75823622984,289698620336,1109059301536, 4253731156128,16342545417760,62885474132992, 242331022479040,935085717105792,3612737418620032, 13974224404904704] |