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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 18 |
| 3 | 170 |
| 4 | 1330 |
| 5 | 11382 |
| 6 | 117810 |
| 7 | 934362 |
| 8 | 8611746 |
| 9 | 82240730 |
| 10 | 699393838 |
| 11 | 6244164940 |
| 12 | 59910383026 |
| 13 | 507902083210 |
| 14 | 4599466921410 |
| 15 | 43063170064620 |
| 16 | 372282144948450 |
| 17 | 3338235118237410 |
| 18 | 31231394376541650 |
| 19 | 270058012725600000 |
[1,2,18,170,1330,11382,117810,934362,8611746, 82240730,699393838,6244164940,59910383026, 507902083210,4599466921410,43063170064620, 372282144948450,3338235118237410, 31231394376541650,270058012725600000] |