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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 28 |
| 5 | 190 |
| 6 | 1730 |
| 7 | 20068 |
| 8 | 287406 |
| 9 | 4971884 |
| 10 | 102082882 |
| 11 | 2450448780 |
| 12 | 67879395878 |
| 13 | 2145912460492 |
| 14 | 76704301481034 |
| 15 | 3075725307199340 |
| 16 | 137422311677357710 |
| 17 | 6800630226338490492 |
| 18 | 370741889753741467970 |
| 19 | 22155195508036869880684 |
| 20 | 1444764915198178824091590 |
[1,1,2,6,28,190,1730,20068,287406,4971884, 102082882,2450448780,67879395878,2145912460492, 76704301481034,3075725307199340, 137422311677357710,6800630226338490492, 370741889753741467970,22155195508036869880684, 1444764915198178824091590] |