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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 0 |
| 7 | 0 |
| 8 | 0 |
| 9 | 1 |
| 10 | 4 |
| 11 | 25 |
| 12 | 108 |
| 13 | 450 |
| 14 | 1713 |
| 15 | 6267 |
| 16 | 21988 |
| 17 | 75185 |
| 18 | 251590 |
| 19 | 828408 |
| 20 | 2692630 |
| 21 | 8661287 |
| 22 | 27624040 |
| 23 | 87479663 |
| 24 | 275392248 |
| 25 | 862593661 |
| 26 | 2690285608 |
| 27 | 8359581585 |
| 28 | 25893044920 |
| 29 | 79978118632 |
| 30 | 246433568617 |
[0,0,0,0,0,0,0,0,1,4,25,108,450,1713,6267,21988, 75185,251590,828408,2692630,8661287,27624040, 87479663,275392248,862593661,2690285608, 8359581585,25893044920,79978118632,246433568617] |