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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 16 |
| 3 | 61 |
| 4 | 304 |
| 5 | 1546 |
| 6 | 8107 |
| 7 | 42748 |
| 8 | 226240 |
| 9 | 1198645 |
| 10 | 6353944 |
| 11 | 33688474 |
| 12 | 178631251 |
| 13 | 947215924 |
| 14 | 5022815920 |
| 15 | 26634734125 |
| 16 | 141237718720 |
| 17 | 748951245034 |
| 18 | 3971518837243 |
| 19 | 21060069709228 |
| 20 | 111676816254688 |
| 21 | 592197081386533 |
| 22 | 3140288211876136 |
[4,16,61,304,1546,8107,42748,226240,1198645, 6353944,33688474,178631251,947215924,5022815920, 26634734125,141237718720,748951245034, 3971518837243,21060069709228,111676816254688, 592197081386533,3140288211876136] |