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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 12 |
| 6 | 44 |
| 7 | 236 |
| 8 | 1644 |
| 9 | 16748 |
| 10 | 227180 |
| 11 | 4514668 |
| 12 | 120830828 |
| 13 | 4743850860 |
| 14 | 252205386604 |
| 15 | 19683018509164 |
| 16 | 2085749545569132 |
| 17 | 324572324799712108 |
| 18 | 68670413434009029484 |
| 19 | 21339842291507941739372 |
| 20 | 9022108271913939454266220 |
[0,1,1,2,4,12,44,236,1644,16748,227180,4514668, 120830828,4743850860,252205386604,19683018509164, 2085749545569132,324572324799712108, 68670413434009029484,21339842291507941739372, 9022108271913939454266220] |