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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 7 |
| 2 | 42 |
| 3 | 252 |
| 4 | 1512 |
| 5 | 9072 |
| 6 | 54432 |
| 7 | 326592 |
| 8 | 1959552 |
| 9 | 11757291 |
| 10 | 70543620 |
| 11 | 423260985 |
| 12 | 2539561500 |
| 13 | 15237342540 |
| 14 | 91423896480 |
| 15 | 548542426320 |
| 16 | 3291248842560 |
| 17 | 19747458763200 |
| 18 | 118484546826660 |
| 19 | 710906046446925 |
| 20 | 4265428871616150 |
[1,7,42,252,1512,9072,54432,326592,1959552, 11757291,70543620,423260985,2539561500, 15237342540,91423896480,548542426320, 3291248842560,19747458763200,118484546826660, 710906046446925,4265428871616150] |