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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 21 |
| 5 | 156 |
| 6 | 1555 |
| 7 | 19608 |
| 8 | 299593 |
| 9 | 5380840 |
| 10 | 111111111 |
| 11 | 2593742460 |
| 12 | 67546215517 |
| 13 | 1941507093540 |
| 14 | 61054982558011 |
| 15 | 2085209001813616 |
| 16 | 76861433640456465 |
| 17 | 3041324492229179280 |
| 18 | 128583032925805678351 |
| 19 | 5784852794328402307380 |
| 20 | 275941052631578947368421 |
[0,1,4,21,156,1555,19608,299593,5380840,111111111, 2593742460,67546215517,1941507093540, 61054982558011,2085209001813616,76861433640456465, 3041324492229179280,128583032925805678351, 5784852794328402307380,275941052631578947368421] |