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| n | a(n) |
|---|---|
| -2 | 1 |
| -1 | 0 |
| 0 | 1 |
| 1 | 2 |
| 2 | 3 |
| 3 | 20 |
| 4 | 23 |
| 5 | 89 |
| 6 | 2871 |
| 7 | 51767 |
| 8 | 158172 |
| 9 | 1317143 |
| 10 | 1475315 |
| 11 | 4267773 |
| 12 | 10010861 |
| 13 | 24289495 |
| 14 | 204326821 |
| 15 | 1045923600 |
| 16 | 2296174021 |
| 17 | 3342097621 |
| 18 | 12322466884 |
| 19 | 27987031389 |
| 20 | 40309498273 |
| 21 | 592320007211 |
| 22 | 1224949512695 |
[1,0,1,2,3,20,23,89,2871,51767,158172,1317143, 1475315,4267773,10010861,24289495,204326821, 1045923600,2296174021,3342097621,12322466884, 27987031389,40309498273,592320007211, 1224949512695] |