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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 18 |
| 3 | 76 |
| 4 | 326 |
| 5 | 1384 |
| 6 | 5892 |
| 7 | 25036 |
| 8 | 106438 |
| 9 | 452344 |
| 10 | 1922588 |
| 11 | 8170936 |
| 12 | 34726940 |
| 13 | 147589264 |
| 14 | 627256088 |
| 15 | 2665837516 |
| 16 | 11329815878 |
| 17 | 48151714264 |
| 18 | 204644809932 |
| 19 | 869740430056 |
| 20 | 3696396920116 |
| 21 | 15709686864304 |
| 22 | 66766169526008 |
| 23 | 283756220309176 |
| 24 | 1205963937666076 |
| 25 | 5125346734404784 |
[1,4,18,76,326,1384,5892,25036,106438,452344, 1922588,8170936,34726940,147589264,627256088, 2665837516,11329815878,48151714264,204644809932, 869740430056,3696396920116,15709686864304, 66766169526008,283756220309176,1205963937666076, 5125346734404784] |