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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 4 |
| 3 | 16 |
| 4 | 112 |
| 5 | 1120 |
| 6 | 14560 |
| 7 | 232960 |
| 8 | 4426240 |
| 9 | 97377280 |
| 10 | 2434432000 |
| 11 | 68164096000 |
| 12 | 2113086976000 |
| 13 | 71844957184000 |
| 14 | 2658263415808000 |
| 15 | 106330536632320000 |
| 16 | 4572213075189760000 |
| 17 | 210321801458728960000 |
| 18 | 10305768271477719040000 |
[1,4,4,16,112,1120,14560,232960,4426240,97377280, 2434432000,68164096000,2113086976000, 71844957184000,2658263415808000, 106330536632320000,4572213075189760000, 210321801458728960000,10305768271477719040000] |