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| n | a(n) |
|---|---|
| 0 | -1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 4 |
| 5 | 10 |
| 6 | 20 |
| 7 | 42 |
| 8 | 84 |
| 9 | 170 |
| 10 | 340 |
| 11 | 682 |
| 12 | 1364 |
| 13 | 2730 |
| 14 | 5460 |
| 15 | 10922 |
| 16 | 21844 |
| 17 | 43690 |
| 18 | 87380 |
| 19 | 174762 |
| 20 | 349524 |
| 21 | 699050 |
| 22 | 1398100 |
| 23 | 2796202 |
| 24 | 5592404 |
| 25 | 11184810 |
| 26 | 22369620 |
| 27 | 44739242 |
| 28 | 89478484 |
| 29 | 178956970 |
| 30 | 357913940 |
| 31 | 715827882 |
[-1,0,0,2,4,10,20,42,84,170,340,682,1364,2730, 5460,10922,21844,43690,87380,174762,349524,699050, 1398100,2796202,5592404,11184810,22369620, 44739242,89478484,178956970,357913940,715827882] |