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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 209 |
| 3 | 1998 |
| 4 | 17157 |
| 5 | 137970 |
| 6 | 1063273 |
| 7 | 7962966 |
| 8 | 58471853 |
| 9 | 423482202 |
| 10 | 3037367697 |
| 11 | 21634921854 |
| 12 | 153344743189 |
| 13 | 1083048862914 |
| 14 | 7630057197881 |
| 15 | 53656123623462 |
| 16 | 376830071424765 |
| 17 | 2644030889883306 |
| 18 | 18539455617424225 |
[1,18,209,1998,17157,137970,1063273,7962966, 58471853,423482202,3037367697,21634921854, 153344743189,1083048862914,7630057197881, 53656123623462,376830071424765,2644030889883306, 18539455617424225] |