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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 15 |
| 5 | 72 |
| 6 | 270 |
| 7 | 1044 |
| 8 | 3795 |
| 9 | 14060 |
| 10 | 51204 |
| 11 | 188604 |
| 12 | 694130 |
| 13 | 2572920 |
| 14 | 9567090 |
| 15 | 35758704 |
| 16 | 134137875 |
| 17 | 505159200 |
| 18 | 1908554190 |
| 19 | 7233104844 |
| 20 | 27486506268 |
| 21 | 104713296760 |
| 22 | 399817262550 |
| 23 | 1529746919604 |
| 24 | 5864041395730 |
| 25 | 22517964582504 |
| 26 | 86607602546220 |
| 27 | 333599838189804 |
| 28 | 1286742419927070 |
| 29 | 4969488707124120 |
| 30 | 19215357085867800 |
[0,0,0,4,15,72,270,1044,3795,14060,51204,188604, 694130,2572920,9567090,35758704,134137875, 505159200,1908554190,7233104844,27486506268, 104713296760,399817262550,1529746919604, 5864041395730,22517964582504,86607602546220, 333599838189804,1286742419927070,4969488707124120, 19215357085867800] |