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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 28 |
| 3 | 232 |
| 4 | 2092 |
| 5 | 19864 |
| 6 | 195352 |
| 7 | 1970896 |
| 8 | 20275660 |
| 9 | 211823836 |
| 10 | 2240798048 |
| 11 | 23951367224 |
| 12 | 258257552968 |
| 13 | 2805581350056 |
| 14 | 30676425237024 |
| 15 | 337324008602512 |
| 16 | 3727882769574860 |
| 17 | 41381900166952348 |
| 18 | 461201577710442388 |
| 19 | 5158610797198820800 |
[1,4,28,232,2092,19864,195352,1970896,20275660, 211823836,2240798048,23951367224,258257552968, 2805581350056,30676425237024,337324008602512, 3727882769574860,41381900166952348, 461201577710442388,5158610797198820800] |