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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 68 |
| 5 | 243 |
| 6 | 970 |
| 7 | 3741 |
| 8 | 15636 |
| 9 | 63207 |
| 10 | 270422 |
| 11 | 1127616 |
| 12 | 4913616 |
| 13 | 20943040 |
| 14 | 92434154 |
| 15 | 400506478 |
| 16 | 1785534204 |
| 17 | 7835181876 |
| 18 | 35208226011 |
| 19 | 156068030420 |
| 20 | 705850854116 |
| 21 | 3154666032504 |
| 22 | 14344306255934 |
| 23 | 64547989929729 |
| 24 | 294831596071278 |
| 25 | 1334358936965836 |
| 26 | 6118522897312851 |
| 27 | 27827559628139189 |
[1,2,6,18,68,243,970,3741,15636,63207,270422, 1127616,4913616,20943040,92434154,400506478, 1785534204,7835181876,35208226011,156068030420, 705850854116,3154666032504,14344306255934, 64547989929729,294831596071278,1334358936965836, 6118522897312851,27827559628139189] |