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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 19 |
| 4 | 100 |
| 5 | 581 |
| 6 | 3912 |
| 7 | 28091 |
| 8 | 211700 |
| 9 | 1655601 |
| 10 | 13286320 |
| 11 | 109058381 |
| 12 | 911436949 |
| 13 | 7731247492 |
[1,4,19,100,581,3912,28091,211700,1655601, 13286320,109058381,911436949,7731247492] |