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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 84 |
| 5 | 740 |
| 6 | 12990 |
| 7 | 201642 |
| 8 | 4475576 |
| 9 | 99719496 |
| 10 | 2735268570 |
| 11 | 78877307630 |
| 12 | 2605450510212 |
| 13 | 91724294787996 |
| 14 | 3563867498039030 |
| 15 | 147715968506783250 |
| 16 | 6618151929336030960 |
| 17 | 315162521018238297872 |
| 18 | 16017517201006303914546 |
| 19 | 861049460872319850568278 |
[1,0,2,6,84,740,12990,201642,4475576,99719496, 2735268570,78877307630,2605450510212, 91724294787996,3563867498039030, 147715968506783250,6618151929336030960, 315162521018238297872,16017517201006303914546, 861049460872319850568278] |