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A123893 as a simple table
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 58 |
| 4 | 208 |
| 5 | 750 |
| 6 | 2708 |
| 7 | 9772 |
| 8 | 35256 |
| 9 | 127210 |
| 10 | 459012 |
| 11 | 1656228 |
| 12 | 5976040 |
| 13 | 21562946 |
| 14 | 77804232 |
| 15 | 280736004 |
| 16 | 1012961416 |
| 17 | 3655002994 |
| 18 | 13188110940 |
| 19 | 47585806908 |
| 20 | 171700784680 |
| 21 | 619536821778 |
| 22 | 2235434596432 |
| 23 | 8065973894524 |
| 24 | 29103931264328 |
| 25 | 105013830473538 |
[1,4,16,58,208,750,2708,9772,35256,127210,459012, 1656228,5976040,21562946,77804232,280736004, 1012961416,3655002994,13188110940,47585806908, 171700784680,619536821778,2235434596432, 8065973894524,29103931264328,105013830473538] |