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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 15 |
| 3 | 90 |
| 4 | 579 |
| 5 | 3858 |
| 6 | 26262 |
| 7 | 181380 |
| 8 | 1265955 |
| 9 | 8906706 |
| 10 | 63058530 |
| 11 | 448716876 |
| 12 | 3206387790 |
| 13 | 22992276180 |
| 14 | 165364807308 |
| 15 | 1192393813320 |
| 16 | 8617219956003 |
| 17 | 62397513984210 |
| 18 | 452607991376490 |
| 19 | 3288138397237884 |
| 20 | 23921128800374874 |
[1,3,15,90,579,3858,26262,181380,1265955,8906706, 63058530,448716876,3206387790,22992276180, 165364807308,1192393813320,8617219956003, 62397513984210,452607991376490,3288138397237884, 23921128800374874] |