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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 18 |
| 3 | 52 |
| 4 | 277 |
| 5 | 1752 |
| 6 | 12120 |
| 7 | 88692 |
| 8 | 674751 |
| 9 | 5282160 |
| 10 | 42267384 |
| 11 | 344152080 |
| 12 | 2842055359 |
| 13 | 23746693240 |
| 14 | 200383750632 |
| 15 | 1705243729560 |
| 16 | 14617677294675 |
| 17 | 126106202849760 |
| 18 | 1094034474058488 |
| 19 | 9538676631305712 |
| 20 | 83536778390997780 |
| 21 | 734521734171474400 |
| 22 | 6481894477750488160 |
[0,0,18,52,277,1752,12120,88692,674751,5282160, 42267384,344152080,2842055359,23746693240, 200383750632,1705243729560,14617677294675, 126106202849760,1094034474058488,9538676631305712, 83536778390997780,734521734171474400, 6481894477750488160] |