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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 8 |
| 3 | 36 |
| 4 | 172 |
| 5 | 852 |
| 6 | 4324 |
| 7 | 22332 |
| 8 | 116876 |
| 9 | 618084 |
| 10 | 3296308 |
| 11 | 17702412 |
| 12 | 95627580 |
| 13 | 519170004 |
| 14 | 2830862532 |
| 15 | 15494401116 |
| 16 | 85091200620 |
| 17 | 468692890308 |
| 18 | 2588521289812 |
| 19 | 14330490031020 |
| 20 | 79509491551772 |
| 21 | 442019710668852 |
[1,2,8,36,172,852,4324,22332,116876,618084, 3296308,17702412,95627580,519170004,2830862532, 15494401116,85091200620,468692890308, 2588521289812,14330490031020,79509491551772, 442019710668852] |