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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 8 |
| 2 | 60 |
| 3 | 444 |
| 4 | 3276 |
| 5 | 24156 |
| 6 | 178092 |
| 7 | 1312956 |
| 8 | 9679500 |
| 9 | 71360028 |
| 10 | 526086252 |
| 11 | 3878455932 |
| 12 | 28593068364 |
| 13 | 210796144092 |
| 14 | 1554048476460 |
| 15 | 11456882559036 |
| 16 | 84463361313804 |
| 17 | 622687661115804 |
| 18 | 4590628614276588 |
| 19 | 33843405595099644 |
| 20 | 249503106984577740 |
| 21 | 1839407095720003932 |
[1,8,60,444,3276,24156,178092,1312956,9679500, 71360028,526086252,3878455932,28593068364, 210796144092,1554048476460,11456882559036, 84463361313804,622687661115804,4590628614276588, 33843405595099644,249503106984577740, 1839407095720003932] |