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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 1 |
| 7 | 2 |
| 8 | 13 |
| 9 | 67 |
| 10 | 404 |
| 11 | 2323 |
| 12 | 13517 |
| 13 | 76570 |
| 14 | 429320 |
| 15 | 2373965 |
| 16 | 13004323 |
| 17 | 70641985 |
| 18 | 381260615 |
| 19 | 2046521491 |
| 20 | 10936624026 |
| 21 | 58228136539 |
[0,0,0,0,0,1,2,13,67,404,2323,13517,76570,429320, 2373965,13004323,70641985,381260615,2046521491, 10936624026,58228136539] |