| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 0 |
| 5 | 2 |
| 6 | 8 |
| 7 | 24 |
| 8 | 70 |
| 9 | 214 |
| 10 | 638 |
| 11 | 1930 |
| 12 | 5782 |
| 13 | 17394 |
| 14 | 52160 |
| 15 | 156620 |
| 16 | 469786 |
| 17 | 1409786 |
| 18 | 4229148 |
| 19 | 12688720 |
| 20 | 38065506 |
| 21 | 114200378 |
| 22 | 342599212 |
| 23 | 1027809200 |
| 24 | 3083421770 |
| 25 | 9250300098 |
| 26 | 27750882922 |
| 27 | 83252753086 |
| 28 | 249758206958 |
| 29 | 749274934114 |
| 30 | 2247824645796 |
| 31 | 6743474876960 |
[0,0,1,0,2,8,24,70,214,638,1930,5782,17394,52160, 156620,469786,1409786,4229148,12688720,38065506, 114200378,342599212,1027809200,3083421770, 9250300098,27750882922,83252753086,249758206958, 749274934114,2247824645796,6743474876960] |