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| n | a(n) |
|---|---|
| 0 | -1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 3 |
| 5 | 6 |
| 6 | 12 |
| 7 | 28 |
| 8 | 71 |
| 9 | 186 |
| 10 | 494 |
| 11 | 1317 |
| 12 | 3478 |
| 13 | 9045 |
| 14 | 23265 |
| 15 | 59856 |
| 16 | 155779 |
| 17 | 412413 |
| 18 | 1108874 |
| 19 | 3009228 |
| 20 | 8188150 |
| 21 | 22257484 |
| 22 | 60462422 |
| 23 | 164715758 |
| 24 | 452011067 |
| 25 | 1253176571 |
[-1,0,1,2,3,6,12,28,71,186,494,1317,3478,9045, 23265,59856,155779,412413,1108874,3009228,8188150, 22257484,60462422,164715758,452011067,1253176571] |