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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | -1 |
| 3 | 0 |
| 4 | 4 |
| 5 | 22 |
| 6 | 78 |
| 7 | 240 |
| 8 | 679 |
| 9 | 1828 |
| 10 | 4762 |
| 11 | 12132 |
| 12 | 30432 |
| 13 | 75504 |
| 14 | 185875 |
| 15 | 455040 |
| 16 | 1109540 |
| 17 | 2697698 |
| 18 | 6545670 |
| 19 | 15859128 |
| 20 | 38384099 |
| 21 | 92832716 |
| 22 | 224399570 |
| 23 | 542226888 |
| 24 | 1309862496 |
| 25 | 3163659744 |
| 26 | 7640066759 |
| 27 | 18448657344 |
| 28 | 44545569508 |
| 29 | 107553559150 |
| 30 | 259675788510 |
[0,-1,0,4,22,78,240,679,1828,4762,12132,30432, 75504,185875,455040,1109540,2697698,6545670, 15859128,38384099,92832716,224399570,542226888, 1309862496,3163659744,7640066759,18448657344, 44545569508,107553559150,259675788510] |