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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 16 |
| 4 | 68 |
| 5 | 256 |
| 6 | 924 |
| 7 | 3232 |
| 8 | 11044 |
| 9 | 37104 |
| 10 | 122984 |
| 11 | 403280 |
| 12 | 1310760 |
| 13 | 4228960 |
| 14 | 13558932 |
| 15 | 43239776 |
| 16 | 137251068 |
| 17 | 433883696 |
| 18 | 1366668772 |
| 19 | 4290998336 |
| 20 | 13433966724 |
| 21 | 41949331616 |
| 22 | 130685405648 |
| 23 | 406258440928 |
| 24 | 1260465716560 |
| 25 | 3903760205760 |
[0,4,16,68,256,924,3232,11044,37104,122984,403280, 1310760,4228960,13558932,43239776,137251068, 433883696,1366668772,4290998336,13433966724, 41949331616,130685405648,406258440928, 1260465716560,3903760205760] |