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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 15 |
| 3 | 54 |
| 4 | 188 |
| 5 | 645 |
| 6 | 2208 |
| 7 | 7570 |
| 8 | 25982 |
| 9 | 89190 |
| 10 | 306095 |
| 11 | 1050268 |
| 12 | 3603276 |
| 13 | 12361763 |
| 14 | 42409154 |
| 15 | 145491117 |
| 16 | 499126660 |
| 17 | 1712311759 |
| 18 | 5874263702 |
| 19 | 20152234481 |
| 20 | 69134134820 |
| 21 | 237171010852 |
| 22 | 813636681973 |
| 23 | 2791253840066 |
| 24 | 9575645985794 |
| 25 | 32850107071454 |
| 26 | 112695214040224 |
[1,4,15,54,188,645,2208,7570,25982,89190,306095, 1050268,3603276,12361763,42409154,145491117, 499126660,1712311759,5874263702,20152234481, 69134134820,237171010852,813636681973, 2791253840066,9575645985794,32850107071454, 112695214040224] |