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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 21 |
| 3 | 126 |
| 4 | 666 |
| 5 | 3996 |
| 6 | 23436 |
| 7 | 140616 |
| 8 | 840456 |
| 9 | 5042736 |
| 10 | 30236976 |
| 11 | 181421856 |
| 12 | 1088414496 |
| 13 | 6530486976 |
| 14 | 39182222016 |
| 15 | 235093332096 |
| 16 | 1410555793536 |
| 17 | 8463334761216 |
| 18 | 50779983373056 |
| 19 | 304679900238336 |
| 20 | 1828079250264576 |
| 21 | 10968475501587456 |
| 22 | 65810852102532096 |
[1,6,21,126,666,3996,23436,140616,840456,5042736, 30236976,181421856,1088414496,6530486976, 39182222016,235093332096,1410555793536, 8463334761216,50779983373056,304679900238336, 1828079250264576,10968475501587456, 65810852102532096] |