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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 34 |
| 4 | 364 |
| 5 | 4269 |
| 6 | 52844 |
| 7 | 679172 |
| 8 | 8976188 |
| 9 | 121223668 |
| 10 | 1665558544 |
| 11 | 23207619274 |
| 12 | 327167316436 |
| 13 | 4657884819670 |
| 14 | 66875794530120 |
| 15 | 967202289590280 |
| 16 | 14077773784645980 |
| 17 | 206058395118133932 |
| 18 | 3031188276557963312 |
| 19 | 44789055557553810152 |
[1,1,4,34,364,4269,52844,679172,8976188,121223668, 1665558544,23207619274,327167316436,4657884819670, 66875794530120,967202289590280,14077773784645980, 206058395118133932,3031188276557963312, 44789055557553810152] |