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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 4 |
| 2 | 14 |
| 3 | 40 |
| 4 | 110 |
| 5 | 304 |
| 6 | 854 |
| 7 | 2440 |
| 8 | 7070 |
| 9 | 20704 |
| 10 | 61094 |
| 11 | 181240 |
| 12 | 539630 |
| 13 | 1610704 |
| 14 | 4815734 |
| 15 | 14414440 |
| 16 | 43177790 |
| 17 | 129402304 |
| 18 | 387944774 |
| 19 | 1163310040 |
| 20 | 3488881550 |
| 21 | 10464547504 |
| 22 | 31389448214 |
| 23 | 94159956040 |
| 24 | 282463090910 |
| 25 | 847355718304 |
[0,4,14,40,110,304,854,2440,7070,20704,61094, 181240,539630,1610704,4815734,14414440,43177790, 129402304,387944774,1163310040,3488881550, 10464547504,31389448214,94159956040,282463090910, 847355718304] |