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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 18 |
| 4 | 81 |
| 5 | 1024 |
| 6 | 7353 |
| 7 | 106056 |
| 8 | 1249592 |
| 9 | 22143847 |
| 10 | 282475249 |
| 11 | 8589934592 |
| 12 | 133642251792 |
| 13 | 3531308221901 |
| 14 | 71789886480657 |
| 15 | 2171807721018968 |
| 16 | 45949729863572161 |
| 17 | 2218611106740436992 |
| 18 | 53241469411989452625 |
[1,4,18,81,1024,7353,106056,1249592,22143847, 282475249,8589934592,133642251792,3531308221901, 71789886480657,2171807721018968,45949729863572161, 2218611106740436992,53241469411989452625] |