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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 28 |
| 4 | 60 |
| 5 | 132 |
| 6 | 300 |
| 7 | 692 |
| 8 | 1596 |
| 9 | 3668 |
| 10 | 8412 |
| 11 | 19284 |
| 12 | 44220 |
| 13 | 101428 |
| 14 | 232668 |
| 15 | 533716 |
| 16 | 1224252 |
| 17 | 2808180 |
| 18 | 6441372 |
| 19 | 14775188 |
| 20 | 33891324 |
| 21 | 77739956 |
| 22 | 178319964 |
| 23 | 409030356 |
| 24 | 938233788 |
| 25 | 2152120564 |
| 26 | 4936534044 |
| 27 | 11323421716 |
| 28 | 25973664636 |
| 29 | 59578391604 |
[1,4,12,28,60,132,300,692,1596,3668,8412,19284, 44220,101428,232668,533716,1224252,2808180, 6441372,14775188,33891324,77739956,178319964, 409030356,938233788,2152120564,4936534044, 11323421716,25973664636,59578391604] |