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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 6 |
| 3 | 20 |
| 4 | 55 |
| 5 | 135 |
| 6 | 308 |
| 7 | 668 |
| 8 | 1395 |
| 9 | 2830 |
| 10 | 5610 |
| 11 | 10914 |
| 12 | 20904 |
| 13 | 39515 |
| 14 | 73860 |
| 15 | 136720 |
| 16 | 250937 |
| 17 | 457137 |
| 18 | 827260 |
| 19 | 1488190 |
| 20 | 2662905 |
| 21 | 4741946 |
| 22 | 8407236 |
| 23 | 14846100 |
| 24 | 26120400 |
| 25 | 45801925 |
| 26 | 80064018 |
| 27 | 139553708 |
| 28 | 242597035 |
| 29 | 420678315 |
| 30 | 727792580 |
[1,6,20,55,135,308,668,1395,2830,5610,10914,20904, 39515,73860,136720,250937,457137,827260,1488190, 2662905,4741946,8407236,14846100,26120400, 45801925,80064018,139553708,242597035,420678315, 727792580] |