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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 4 |
| 3 | 12 |
| 4 | 34 |
| 5 | 110 |
| 6 | 354 |
| 7 | 1120 |
| 8 | 3552 |
| 9 | 11290 |
| 10 | 35862 |
| 11 | 113884 |
| 12 | 361702 |
| 13 | 1148810 |
| 14 | 3648670 |
| 15 | 11588338 |
| 16 | 36805222 |
| 17 | 116895404 |
| 18 | 371266018 |
| 19 | 1179160836 |
| 20 | 3745078428 |
| 21 | 11894570660 |
| 22 | 37777796510 |
| 23 | 119984315496 |
| 24 | 381076645196 |
| 25 | 1210319938646 |
| 26 | 3844041278068 |
| 27 | 12208882029838 |
[0,0,4,12,34,110,354,1120,3552,11290,35862,113884, 361702,1148810,3648670,11588338,36805222, 116895404,371266018,1179160836,3745078428, 11894570660,37777796510,119984315496,381076645196, 1210319938646,3844041278068,12208882029838] |