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| n | a(n) |
|---|---|
| 0 | -2 |
| 1 | 0 |
| 2 | -1 |
| 3 | 1 |
| 4 | 5 |
| 5 | 18 |
| 6 | 52 |
| 7 | 140 |
| 8 | 361 |
| 9 | 909 |
| 10 | 2255 |
| 11 | 5542 |
| 12 | 13538 |
| 13 | 32940 |
| 14 | 79939 |
| 15 | 193661 |
| 16 | 468625 |
| 17 | 1133118 |
| 18 | 2738432 |
| 19 | 6615760 |
| 20 | 15979301 |
| 21 | 38589489 |
| 22 | 93182755 |
| 23 | 224994602 |
| 24 | 543236038 |
| 25 | 1311570360 |
| 26 | 3166544519 |
| 27 | 7644930841 |
| 28 | 18456845405 |
| 29 | 44559332298 |
[-2,0,-1,1,5,18,52,140,361,909,2255,5542,13538, 32940,79939,193661,468625,1133118,2738432,6615760, 15979301,38589489,93182755,224994602,543236038, 1311570360,3166544519,7644930841,18456845405, 44559332298] |