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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 15 |
| 4 | 327 |
| 5 | 4856 |
| 6 | 53455 |
| 7 | 444003 |
| 8 | 2948305 |
| 9 | 16112289 |
| 10 | 75389116 |
| 11 | 307372600 |
| 12 | 1122069080 |
| 13 | 3701885580 |
| 14 | 11258893954 |
| 15 | 31699979961 |
| 16 | 83910860201 |
| 17 | 209004408715 |
| 18 | 496246703439 |
| 19 | 1121475446118 |
| 20 | 2440154664350 |
| 21 | 5096346969372 |
| 22 | 10323359668079 |
[0,1,15,327,4856,53455,444003,2948305,16112289, 75389116,307372600,1122069080,3701885580, 11258893954,31699979961,83910860201,209004408715, 496246703439,1121475446118,2440154664350, 5096346969372,10323359668079] |