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| n | a(n) |
|---|---|
| 1 | 180 |
| 2 | 714 |
| 3 | 2880 |
| 4 | 12318 |
| 5 | 53100 |
| 6 | 230532 |
| 7 | 1002240 |
| 8 | 4361064 |
| 9 | 18980472 |
| 10 | 82617132 |
| 11 | 359622708 |
| 12 | 1565418528 |
| 13 | 6814215036 |
| 14 | 29662110636 |
| 15 | 129118523304 |
| 16 | 562050276348 |
| 17 | 2446593518052 |
| 18 | 10649972628456 |
| 19 | 46359118343628 |
| 20 | 201800318106108 |
[180,714,2880,12318,53100,230532,1002240,4361064, 18980472,82617132,359622708,1565418528,6814215036, 29662110636,129118523304,562050276348, 2446593518052,10649972628456,46359118343628, 201800318106108] |