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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 6 |
| 3 | 41 |
| 4 | 306 |
| 5 | 2426 |
| 6 | 20076 |
| 7 | 171481 |
| 8 | 1500666 |
| 9 | 13386206 |
| 10 | 121267476 |
| 11 | 1112674026 |
| 12 | 10318939956 |
| 13 | 96572168916 |
| 14 | 910896992856 |
| 15 | 8650566601401 |
| 16 | 82644968321226 |
| 17 | 793753763514806 |
| 18 | 7659535707782916 |
| 19 | 74225795172589006 |
| 20 | 722042370787826076 |
[0,1,6,41,306,2426,20076,171481,1500666,13386206, 121267476,1112674026,10318939956,96572168916, 910896992856,8650566601401,82644968321226, 793753763514806,7659535707782916, 74225795172589006,722042370787826076] |