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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 26 |
| 4 | 188 |
| 5 | 1499 |
| 6 | 12628 |
| 7 | 111064 |
| 8 | 1006840 |
| 9 | 9345761 |
| 10 | 88371580 |
| 11 | 848273424 |
| 12 | 8244075700 |
| 13 | 80959901281 |
| 14 | 802137370804 |
| 15 | 8008422811882 |
| 16 | 80488941119484 |
| 17 | 813703130213745 |
| 18 | 8268866850613468 |
| 19 | 84417609311862182 |
| 20 | 865408913186449784 |
| 21 | 8905028017997573696 |
[0,1,4,26,188,1499,12628,111064,1006840,9345761, 88371580,848273424,8244075700,80959901281, 802137370804,8008422811882,80488941119484, 813703130213745,8268866850613468, 84417609311862182,865408913186449784, 8905028017997573696] |