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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 40 |
| 5 | 142 |
| 6 | 542 |
| 7 | 2051 |
| 8 | 7968 |
| 9 | 31878 |
| 10 | 129379 |
| 11 | 526590 |
| 12 | 2177011 |
| 13 | 9114403 |
| 14 | 38339372 |
| 15 | 162138828 |
| 16 | 692133302 |
| 17 | 2971530483 |
| 18 | 12797863155 |
| 19 | 55397548914 |
| 20 | 241112647433 |
| 21 | 1052700933509 |
| 22 | 4609346635549 |
| 23 | 20262348466798 |
| 24 | 89364098150685 |
| 25 | 394999047315331 |
| 26 | 1750471906940722 |
| 27 | 7779534818923431 |
[1,1,4,12,40,142,542,2051,7968,31878,129379, 526590,2177011,9114403,38339372,162138828, 692133302,2971530483,12797863155,55397548914, 241112647433,1052700933509,4609346635549, 20262348466798,89364098150685,394999047315331, 1750471906940722,7779534818923431] |