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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 42 |
| 5 | 157 |
| 6 | 637 |
| 7 | 2501 |
| 8 | 10164 |
| 9 | 42658 |
| 10 | 180400 |
| 11 | 764722 |
| 12 | 3307143 |
| 13 | 14430374 |
| 14 | 62996763 |
| 15 | 276911209 |
| 16 | 1228976451 |
| 17 | 5469146618 |
| 18 | 24404767964 |
| 19 | 109552267142 |
| 20 | 493669549335 |
| 21 | 2227647563738 |
| 22 | 10084056179245 |
| 23 | 45818706625373 |
| 24 | 208578109286625 |
| 25 | 951168969946909 |
| 26 | 4349255976194362 |
| 27 | 19927255165939965 |
[1,1,4,12,42,157,637,2501,10164,42658,180400, 764722,3307143,14430374,62996763,276911209, 1228976451,5469146618,24404767964,109552267142, 493669549335,2227647563738,10084056179245, 45818706625373,208578109286625,951168969946909, 4349255976194362,19927255165939965] |