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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 96 |
| 5 | 780 |
| 6 | 4080 |
| 7 | 15330 |
| 8 | 45696 |
| 9 | 115416 |
| 10 | 257760 |
| 11 | 523710 |
| 12 | 987360 |
| 13 | 1752036 |
| 14 | 2957136 |
| 15 | 4785690 |
| 16 | 7472640 |
| 17 | 11313840 |
| 18 | 16675776 |
| 19 | 24006006 |
| 20 | 33844320 |
| 21 | 46834620 |
| 22 | 63737520 |
| 23 | 85443666 |
| 24 | 112987776 |
| 25 | 147563400 |
| 26 | 190538400 |
| 27 | 243471150 |
| 28 | 308127456 |
[0,0,0,6,96,780,4080,15330,45696,115416,257760, 523710,987360,1752036,2957136,4785690,7472640, 11313840,16675776,24006006,33844320,46834620, 63737520,85443666,112987776,147563400,190538400, 243471150,308127456] |