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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 22 |
| 3 | 146 |
| 4 | 1079 |
| 5 | 8525 |
| 6 | 70468 |
| 7 | 601816 |
| 8 | 5268241 |
| 9 | 47019566 |
| 10 | 426250277 |
| 11 | 3914020148 |
| 12 | 36328457669 |
| 13 | 340278596273 |
| 14 | 3212416054283 |
| 15 | 30534649412247 |
| 16 | 291981031204917 |
| 17 | 2806832429353512 |
| 18 | 27109863184695640 |
| 19 | 262951127248539898 |
| 20 | 2560229132085602215 |
[1,4,22,146,1079,8525,70468,601816,5268241, 47019566,426250277,3914020148,36328457669, 340278596273,3212416054283,30534649412247, 291981031204917,2806832429353512, 27109863184695640,262951127248539898, 2560229132085602215] |