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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 2 |
| 4 | 0 |
| 5 | 6 |
| 6 | 12 |
| 7 | 6 |
| 8 | 0 |
| 9 | 20 |
| 10 | 40 |
| 11 | 20 |
| 12 | 0 |
| 13 | 70 |
| 14 | 140 |
| 15 | 70 |
| 16 | 0 |
| 17 | 252 |
| 18 | 504 |
| 19 | 252 |
| 20 | 0 |
| 21 | 924 |
| 22 | 1848 |
| 23 | 924 |
| 24 | 0 |
| 25 | 3432 |
| 26 | 6864 |
| 27 | 3432 |
| 28 | 0 |
| 29 | 12870 |
| 30 | 25740 |
| 31 | 12870 |
| 32 | 0 |
| 33 | 48620 |
| 34 | 97240 |
| 35 | 48620 |
| 36 | 0 |
| 37 | 184756 |
| 38 | 369512 |
| 39 | 184756 |
| 40 | 0 |
| 41 | 705432 |
| 42 | 1410864 |
| 43 | 705432 |
| 44 | 0 |
| 45 | 2704156 |
| 46 | 5408312 |
| 47 | 2704156 |
| 48 | 0 |
| 49 | 10400600 |
[2,4,2,0,6,12,6,0,20,40,20,0,70,140,70,0,252,504, 252,0,924,1848,924,0,3432,6864,3432,0,12870,25740, 12870,0,48620,97240,48620,0,184756,369512,184756, 0,705432,1410864,705432,0,2704156,5408312,2704156, 0,10400600] |