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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 142 |
| 3 | 918 |
| 4 | 6902 |
| 5 | 52818 |
| 6 | 413974 |
| 7 | 3289290 |
| 8 | 26413814 |
| 9 | 213785910 |
| 10 | 1740901972 |
| 11 | 14244084664 |
| 12 | 116982000962 |
| 13 | 963573445450 |
| 14 | 7955405806616 |
| 15 | 65801903210688 |
| 16 | 545060017403430 |
| 17 | 4520080784608610 |
| 18 | 37517875619404780 |
| 19 | 311628272467347236 |
[1,18,142,918,6902,52818,413974,3289290,26413814, 213785910,1740901972,14244084664,116982000962, 963573445450,7955405806616,65801903210688, 545060017403430,4520080784608610, 37517875619404780,311628272467347236] |