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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 16 |
| 3 | 216 |
| 4 | 710 |
| 5 | 3648 |
| 6 | 25642 |
| 7 | 139456 |
| 8 | 683250 |
| 9 | 3950740 |
| 10 | 22616130 |
| 11 | 120525288 |
| 12 | 658213410 |
| 13 | 3693117580 |
| 14 | 20305930298 |
| 15 | 110933224304 |
| 16 | 613037501594 |
| 17 | 3386085231380 |
| 18 | 18604669612418 |
| 19 | 102411236923656 |
| 20 | 564815468453874 |
[4,16,216,710,3648,25642,139456,683250,3950740, 22616130,120525288,658213410,3693117580, 20305930298,110933224304,613037501594, 3386085231380,18604669612418,102411236923656, 564815468453874] |