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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 3 |
| 2 | 6 |
| 3 | 27 |
| 4 | 84 |
| 5 | 303 |
| 6 | 1026 |
| 7 | 3567 |
| 8 | 12264 |
| 9 | 42363 |
| 10 | 146046 |
| 11 | 503907 |
| 12 | 1738044 |
| 13 | 5995623 |
| 14 | 20681466 |
| 15 | 71341047 |
| 16 | 246089424 |
| 17 | 848884083 |
| 18 | 2928215286 |
| 19 | 10100850987 |
| 20 | 34842778404 |
| 21 | 120189811743 |
| 22 | 414593515506 |
| 23 | 1430136089727 |
| 24 | 4933239756984 |
| 25 | 17017159962603 |
| 26 | 58700518710126 |
[0,3,6,27,84,303,1026,3567,12264,42363,146046, 503907,1738044,5995623,20681466,71341047, 246089424,848884083,2928215286,10100850987, 34842778404,120189811743,414593515506, 1430136089727,4933239756984,17017159962603, 58700518710126] |