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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 3 |
| 6 | 10 |
| 7 | 30 |
| 8 | 88 |
| 9 | 255 |
| 10 | 742 |
| 11 | 2157 |
| 12 | 6312 |
| 13 | 18563 |
| 14 | 54932 |
| 15 | 163479 |
| 16 | 489264 |
| 17 | 1471692 |
| 18 | 4447896 |
| 19 | 13500689 |
| 20 | 41140608 |
| 21 | 125818217 |
| 22 | 386050543 |
| 23 | 1188093392 |
| 24 | 3666547089 |
| 25 | 11344058829 |
| 26 | 35180323336 |
| 27 | 109339097119 |
| 28 | 340508394528 |
[0,0,0,1,3,10,30,88,255,742,2157,6312,18563,54932, 163479,489264,1471692,4447896,13500689,41140608, 125818217,386050543,1188093392,3666547089, 11344058829,35180323336,109339097119,340508394528] |