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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 21 |
| 3 | 127 |
| 4 | 749 |
| 5 | 4455 |
| 6 | 26725 |
| 7 | 161007 |
| 8 | 971613 |
| 9 | 5866487 |
| 10 | 35426517 |
| 11 | 213940607 |
| 12 | 1291991757 |
| 13 | 7802356615 |
| 14 | 47118492485 |
| 15 | 284548794383 |
[4,21,127,749,4455,26725,161007,971613,5866487, 35426517,213940607,1291991757,7802356615, 47118492485,284548794383] |