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| n | a(n) |
|---|---|
| 0 | 4 |
| 1 | 15 |
| 2 | 91 |
| 3 | 612 |
| 4 | 4183 |
| 5 | 28659 |
| 6 | 196420 |
| 7 | 1346271 |
| 8 | 9227467 |
| 9 | 63245988 |
| 10 | 433494439 |
| 11 | 2971215075 |
| 12 | 20365011076 |
| 13 | 139583862447 |
| 14 | 956722026043 |
| 15 | 6557470319844 |
| 16 | 44945570212855 |
| 17 | 308061521170131 |
| 18 | 2111485077978052 |
| 19 | 14472334024676223 |
[4,15,91,612,4183,28659,196420,1346271,9227467, 63245988,433494439,2971215075,20365011076, 139583862447,956722026043,6557470319844, 44945570212855,308061521170131,2111485077978052, 14472334024676223] |