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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | -1 |
| 2 | 2 |
| 3 | 2 |
| 4 | 9 |
| 5 | 20 |
| 6 | 56 |
| 7 | 143 |
| 8 | 378 |
| 9 | 986 |
| 10 | 2585 |
| 11 | 6764 |
| 12 | 17712 |
| 13 | 46367 |
| 14 | 121394 |
| 15 | 317810 |
| 16 | 832041 |
| 17 | 2178308 |
| 18 | 5702888 |
| 19 | 14930351 |
| 20 | 39088170 |
| 21 | 102334154 |
| 22 | 267914297 |
| 23 | 701408732 |
| 24 | 1836311904 |
| 25 | 4807526975 |
| 26 | 12586269026 |
| 27 | 32951280098 |
| 28 | 86267571273 |
| 29 | 225851433716 |
| 30 | 591286729880 |
[0,-1,2,2,9,20,56,143,378,986,2585,6764,17712, 46367,121394,317810,832041,2178308,5702888, 14930351,39088170,102334154,267914297,701408732, 1836311904,4807526975,12586269026,32951280098, 86267571273,225851433716,591286729880] |