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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 4 |
| 3 | 20 |
| 4 | 97 |
| 5 | 468 |
| 6 | 2256 |
| 7 | 10876 |
| 8 | 52447 |
| 9 | 252984 |
| 10 | 1220580 |
| 11 | 5890044 |
| 12 | 28427026 |
| 13 | 137211432 |
| 14 | 662344528 |
| 15 | 3197451224 |
| 16 | 15436322843 |
| 17 | 74524477168 |
| 18 | 359803660284 |
| 19 | 1737164916028 |
| 20 | 8387321609038 |
| 21 | 40495871783624 |
| 22 | 195524970070848 |
| 23 | 944053945629128 |
| 24 | 4558204500847574 |
[1,0,4,20,97,468,2256,10876,52447,252984,1220580, 5890044,28427026,137211432,662344528,3197451224, 15436322843,74524477168,359803660284, 1737164916028,8387321609038,40495871783624, 195524970070848,944053945629128,4558204500847574] |