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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 4 |
| 3 | 6 |
| 4 | 32 |
| 5 | 130 |
| 6 | 432 |
| 7 | 1274 |
| 8 | 3488 |
| 9 | 9090 |
| 10 | 22880 |
| 11 | 56122 |
| 12 | 134928 |
| 13 | 319202 |
| 14 | 745136 |
| 15 | 1719930 |
| 16 | 3931712 |
| 17 | 8912386 |
| 18 | 20053440 |
| 19 | 44825978 |
| 20 | 99614000 |
| 21 | 220200162 |
| 22 | 484441232 |
| 23 | 1061157946 |
| 24 | 2315254752 |
| 25 | 5033163650 |
| 26 | 10905189152 |
| 27 | 23555209914 |
| 28 | 50734299728 |
| 29 | 108984793570 |
[1,0,4,6,32,130,432,1274,3488,9090,22880,56122, 134928,319202,745136,1719930,3931712,8912386, 20053440,44825978,99614000,220200162,484441232, 1061157946,2315254752,5033163650,10905189152, 23555209914,50734299728,108984793570] |