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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 0 |
| 3 | 0 |
| 4 | 165 |
| 5 | 674 |
| 6 | 3770 |
| 7 | 15100 |
| 8 | 172590 |
| 9 | 759758 |
| 10 | 6657106 |
| 11 | 30994294 |
| 12 | 298933498 |
| 13 | 1368656291 |
| 14 | 12779873412 |
| 15 | 59202186592 |
| 16 | 560870492027 |
| 17 | 2605855916653 |
| 18 | 24609622243330 |
| 19 | 114661599066810 |
| 20 | 1086770275159481 |
| 21 | 5073242396321810 |
[4,0,0,165,674,3770,15100,172590,759758,6657106, 30994294,298933498,1368656291,12779873412, 59202186592,560870492027,2605855916653, 24609622243330,114661599066810,1086770275159481, 5073242396321810] |