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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 0 |
| 4 | 3 |
| 5 | 4 |
| 6 | 27 |
| 7 | 68 |
| 8 | 315 |
| 9 | 980 |
| 10 | 3883 |
| 11 | 13188 |
| 12 | 49355 |
| 13 | 173716 |
| 14 | 635483 |
| 15 | 2268676 |
| 16 | 8224667 |
| 17 | 29529044 |
| 18 | 106669131 |
| 19 | 383840260 |
| 20 | 1384587819 |
| 21 | 4986809492 |
| 22 | 17978203387 |
| 23 | 64774493572 |
| 24 | 233469116027 |
| 25 | 841296459988 |
| 26 | 3032043498091 |
| 27 | 10926465128068 |
| 28 | 39377714668171 |
| 29 | 141907245404308 |
[0,1,0,3,4,27,68,315,980,3883,13188,49355,173716, 635483,2268676,8224667,29529044,106669131, 383840260,1384587819,4986809492,17978203387, 64774493572,233469116027,841296459988, 3032043498091,10926465128068,39377714668171, 141907245404308] |