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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 2 |
| 3 | 4 |
| 4 | 8 |
| 5 | 20 |
| 6 | 60 |
| 7 | 216 |
| 8 | 898 |
| 9 | 4174 |
| 10 | 21202 |
| 11 | 116064 |
| 12 | 678714 |
| 13 | 4213830 |
| 14 | 27644814 |
| 15 | 190899932 |
| 16 | 1382959532 |
| 17 | 10480143744 |
| 18 | 82864872388 |
| 19 | 682076810340 |
| 20 | 5832742211822 |
| 21 | 51724158246318 |
| 22 | 474869816174462 |
| 23 | 4506715738475980 |
[1,2,2,4,8,20,60,216,898,4174,21202,116064,678714, 4213830,27644814,190899932,1382959532,10480143744, 82864872388,682076810340,5832742211822, 51724158246318,474869816174462,4506715738475980] |