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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 0 |
| 3 | 20 |
| 4 | 12 |
| 5 | 572 |
| 6 | 2348 |
| 7 | 22152 |
| 8 | 129230 |
| 9 | 915192 |
| 10 | 5625202 |
| 11 | 37271957 |
| 12 | 233347958 |
| 13 | 1512344735 |
| 14 | 9550825980 |
| 15 | 61315204660 |
| 16 | 389091647972 |
| 17 | 2487355416820 |
| 18 | 15822559226124 |
| 19 | 100953094987052 |
| 20 | 642909203731360 |
| 21 | 4098621203473156 |
[2,0,20,12,572,2348,22152,129230,915192,5625202, 37271957,233347958,1512344735,9550825980, 61315204660,389091647972,2487355416820, 15822559226124,100953094987052,642909203731360, 4098621203473156] |