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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | -1 |
| 2 | -1 |
| 3 | 3 |
| 4 | 10 |
| 5 | 14 |
| 6 | 19 |
| 7 | 64 |
| 8 | 228 |
| 9 | 620 |
| 10 | 1488 |
| 11 | 3700 |
| 12 | 9845 |
| 13 | 26445 |
| 14 | 69490 |
| 15 | 180428 |
| 16 | 470197 |
| 17 | 1232747 |
| 18 | 3234809 |
| 19 | 8471680 |
| 20 | 22162520 |
| 21 | 57998169 |
| 22 | 151860644 |
| 23 | 397658788 |
| 24 | 1041115720 |
| 25 | 2725491954 |
| 26 | 7135163724 |
| 27 | 18680317029 |
| 28 | 48906619403 |
| 29 | 128039541180 |
| 30 | 335209825828 |
| 31 | 877587757995 |
[1,-1,-1,3,10,14,19,64,228,620,1488,3700,9845, 26445,69490,180428,470197,1232747,3234809,8471680, 22162520,57998169,151860644,397658788,1041115720, 2725491954,7135163724,18680317029,48906619403, 128039541180,335209825828,877587757995] |