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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 10 |
| 3 | 60 |
| 4 | 430 |
| 5 | 3396 |
| 6 | 28818 |
| 7 | 256172 |
| 8 | 2357138 |
| 9 | 22253672 |
| 10 | 214370398 |
| 11 | 2098593628 |
| 12 | 20817790876 |
| 13 | 208801698676 |
| 14 | 2113957366698 |
| 15 | 21574762692484 |
| 16 | 221729081428478 |
| 17 | 2292720460828372 |
| 18 | 23835381083324608 |
| 19 | 248987501825970604 |
| 20 | 2612160344953154508 |
| 21 | 27510833867426222908 |
[4,10,60,430,3396,28818,256172,2357138,22253672, 214370398,2098593628,20817790876,208801698676, 2113957366698,21574762692484,221729081428478, 2292720460828372,23835381083324608, 248987501825970604,2612160344953154508, 27510833867426222908] |