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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 12 |
| 5 | 36 |
| 6 | 117 |
| 7 | 351 |
| 8 | 1080 |
| 9 | 3240 |
| 10 | 9801 |
| 11 | 29403 |
| 12 | 88452 |
| 13 | 265356 |
| 14 | 796797 |
| 15 | 2390391 |
| 16 | 7173360 |
| 17 | 21520080 |
| 18 | 64566801 |
| 19 | 193700403 |
| 20 | 581120892 |
| 21 | 1743362676 |
| 22 | 5230147077 |
| 23 | 15690441231 |
| 24 | 47071500840 |
| 25 | 141214502520 |
| 26 | 423644039001 |
| 27 | 1270932117003 |
| 28 | 3812797945332 |
| 29 | 11438393835996 |
[0,0,1,3,12,36,117,351,1080,3240,9801,29403,88452, 265356,796797,2390391,7173360,21520080,64566801, 193700403,581120892,1743362676,5230147077, 15690441231,47071500840,141214502520,423644039001, 1270932117003,3812797945332,11438393835996] |