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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 22 |
| 3 | 118 |
| 4 | 610 |
| 5 | 3094 |
| 6 | 15562 |
| 7 | 77998 |
| 8 | 390370 |
| 9 | 1952614 |
| 10 | 9764602 |
| 11 | 48826078 |
| 12 | 244136530 |
| 13 | 1220694934 |
| 14 | 6103499242 |
| 15 | 30517545358 |
| 16 | 152587825090 |
| 17 | 762939322054 |
| 18 | 3814697003482 |
| 19 | 19073485803838 |
| 20 | 95367430592050 |
| 21 | 476837156105974 |
[1,4,22,118,610,3094,15562,77998,390370,1952614, 9764602,48826078,244136530,1220694934,6103499242, 30517545358,152587825090,762939322054, 3814697003482,19073485803838,95367430592050, 476837156105974] |