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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 7 |
| 4 | 25 |
| 5 | 72 |
| 6 | 278 |
| 7 | 918 |
| 8 | 3678 |
| 9 | 13040 |
| 10 | 53884 |
| 11 | 200694 |
| 12 | 845723 |
| 13 | 3266873 |
| 14 | 13972607 |
| 15 | 55450557 |
| 16 | 240031808 |
| 17 | 972983451 |
| 18 | 4251703434 |
| 19 | 17532731134 |
| 20 | 77217505713 |
| 21 | 322913991532 |
| 22 | 1431620492774 |
| 23 | 6057640157681 |
| 24 | 27007621918993 |
| 25 | 115423839180006 |
| 26 | 517127199750207 |
| 27 | 2229091048295270 |
| 28 | 10029555035534357 |
[1,1,3,7,25,72,278,918,3678,13040,53884,200694, 845723,3266873,13972607,55450557,240031808, 972983451,4251703434,17532731134,77217505713, 322913991532,1431620492774,6057640157681, 27007621918993,115423839180006,517127199750207, 2229091048295270,10029555035534357] |