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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 4 |
| 4 | 4 |
| 5 | 36 |
| 6 | 88 |
| 7 | 432 |
| 8 | 1408 |
| 9 | 5776 |
| 10 | 20736 |
| 11 | 80320 |
| 12 | 297792 |
| 13 | 1132096 |
| 14 | 4242304 |
| 15 | 16028928 |
| 16 | 60276736 |
| 17 | 227287296 |
| 18 | 855703552 |
| 19 | 3224482816 |
| 20 | 12144337920 |
| 21 | 45752574976 |
| 22 | 172339107840 |
| 23 | 649223532544 |
| 24 | 2445572276224 |
| 25 | 9212566081536 |
| 26 | 34703459811328 |
[1,0,4,4,36,88,432,1408,5776,20736,80320,297792, 1132096,4242304,16028928,60276736,227287296, 855703552,3224482816,12144337920,45752574976, 172339107840,649223532544,2445572276224, 9212566081536,34703459811328] |