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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 24 |
| 5 | 60 |
| 6 | 141 |
| 7 | 354 |
| 8 | 996 |
| 9 | 2720 |
| 10 | 7194 |
| 11 | 18306 |
| 12 | 46154 |
| 13 | 115506 |
| 14 | 288195 |
| 15 | 713210 |
| 16 | 1749732 |
| 17 | 4253148 |
| 18 | 10259302 |
| 19 | 24573390 |
| 20 | 58491312 |
| 21 | 138371354 |
| 22 | 325415727 |
| 23 | 760899396 |
| 24 | 1769420183 |
| 25 | 4093054602 |
| 26 | 9420739965 |
| 27 | 21578842582 |
| 28 | 49199229066 |
| 29 | 111672215658 |
| 30 | 252381169048 |
[1,0,0,6,24,60,141,354,996,2720,7194,18306,46154, 115506,288195,713210,1749732,4253148,10259302, 24573390,58491312,138371354,325415727,760899396, 1769420183,4093054602,9420739965,21578842582, 49199229066,111672215658,252381169048] |