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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 16 |
| 3 | 116 |
| 4 | 1038 |
| 5 | 10922 |
| 6 | 131256 |
| 7 | 1766592 |
| 8 | 26253702 |
| 9 | 426173906 |
| 10 | 7492270416 |
| 11 | 141661870088 |
| 12 | 2864168171596 |
| 13 | 61621248390756 |
| 14 | 1404853103594128 |
| 15 | 33815954626749600 |
| 16 | 856680253728250950 |
| 17 | 22777071459869216850 |
| 18 | 633968368216974945600 |
| 19 | 18430976777427663053400 |
[1,3,16,116,1038,10922,131256,1766592,26253702, 426173906,7492270416,141661870088,2864168171596, 61621248390756,1404853103594128,33815954626749600, 856680253728250950,22777071459869216850, 633968368216974945600,18430976777427663053400] |