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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 56 |
| 5 | 194 |
| 6 | 936 |
| 7 | 3538 |
| 8 | 17321 |
| 9 | 68903 |
| 10 | 339902 |
| 11 | 1396514 |
| 12 | 6919349 |
| 13 | 29062278 |
| 14 | 144387889 |
| 15 | 616244809 |
| 16 | 3067086814 |
| 17 | 13251144642 |
| 18 | 66031397048 |
| 19 | 288051494440 |
| 20 | 1436595469141 |
| 21 | 6316268935590 |
| 22 | 31520173742537 |
| 23 | 139490497666088 |
| 24 | 696411055283854 |
| 25 | 3098956054640149 |
| 26 | 15476764066529596 |
| 27 | 69196679300334168 |
[1,1,4,12,56,194,936,3538,17321,68903,339902, 1396514,6919349,29062278,144387889,616244809, 3067086814,13251144642,66031397048,288051494440, 1436595469141,6316268935590,31520173742537, 139490497666088,696411055283854,3098956054640149, 15476764066529596,69196679300334168] |