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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 4 |
| 3 | 6 |
| 4 | 30 |
| 5 | 80 |
| 6 | 286 |
| 7 | 882 |
| 8 | 2924 |
| 9 | 9350 |
| 10 | 30438 |
| 11 | 98208 |
| 12 | 318278 |
| 13 | 1029210 |
| 14 | 3331820 |
| 15 | 10780014 |
| 16 | 34888062 |
| 17 | 112894960 |
| 18 | 365344142 |
| 19 | 1182264930 |
| 20 | 3825911596 |
| 21 | 12380874550 |
| 22 | 40065409014 |
| 23 | 129654294336 |
| 24 | 419570260150 |
| 25 | 1357757640330 |
[1,0,4,6,30,80,286,882,2924,9350,30438,98208, 318278,1029210,3331820,10780014,34888062, 112894960,365344142,1182264930,3825911596, 12380874550,40065409014,129654294336,419570260150, 1357757640330] |