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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 10 |
| 4 | 26 |
| 5 | 69 |
| 6 | 184 |
| 7 | 488 |
| 8 | 1294 |
| 9 | 3436 |
| 10 | 9116 |
| 11 | 24190 |
| 12 | 64190 |
| 13 | 170334 |
| 14 | 451994 |
| 15 | 1199400 |
| 16 | 3182706 |
| 17 | 8445556 |
| 18 | 22410946 |
| 19 | 59469200 |
| 20 | 157806184 |
| 21 | 418751069 |
| 22 | 1111188772 |
| 23 | 2948626472 |
| 24 | 7824411358 |
| 25 | 20762688580 |
| 26 | 55095420880 |
| 27 | 146200015984 |
[1,1,4,10,26,69,184,488,1294,3436,9116,24190, 64190,170334,451994,1199400,3182706,8445556, 22410946,59469200,157806184,418751069,1111188772, 2948626472,7824411358,20762688580,55095420880, 146200015984] |