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| n | a(n) |
|---|---|
| 1 | -1 |
| 2 | 1 |
| 3 | 5 |
| 4 | 20 |
| 5 | 77 |
| 6 | 294 |
| 7 | 1122 |
| 8 | 4290 |
| 9 | 16445 |
| 10 | 63206 |
| 11 | 243542 |
| 12 | 940576 |
| 13 | 3640210 |
| 14 | 14115100 |
| 15 | 54826020 |
| 16 | 213286590 |
| 17 | 830905245 |
| 18 | 3241119750 |
| 19 | 12657425550 |
| 20 | 49483369320 |
| 21 | 193641552390 |
| 22 | 758454277620 |
| 23 | 2973183318300 |
| 24 | 11664026864100 |
| 25 | 45791597230002 |
| 26 | 179892016853724 |
[-1,1,5,20,77,294,1122,4290,16445,63206,243542, 940576,3640210,14115100,54826020,213286590, 830905245,3241119750,12657425550,49483369320, 193641552390,758454277620,2973183318300, 11664026864100,45791597230002,179892016853724] |