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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 13 |
| 6 | 31 |
| 7 | 140 |
| 8 | 480 |
| 9 | 2306 |
| 10 | 9179 |
| 11 | 58209 |
| 12 | 249205 |
| 13 | 1802970 |
| 14 | 9463155 |
| 15 | 63813439 |
| 16 | 389176317 |
| 17 | 3415876088 |
| 18 | 20506436732 |
| 19 | 195865505549 |
| 20 | 1353967583125 |
| 21 | 12006363947433 |
| 22 | 93067012435816 |
| 23 | 1019489483393439 |
[1,1,1,2,4,13,31,140,480,2306,9179,58209,249205, 1802970,9463155,63813439,389176317,3415876088, 20506436732,195865505549,1353967583125, 12006363947433,93067012435816,1019489483393439] |