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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 16 |
| 3 | 58 |
| 4 | 204 |
| 5 | 712 |
| 6 | 2490 |
| 7 | 8770 |
| 8 | 31200 |
| 9 | 112300 |
| 10 | 409254 |
| 11 | 1510102 |
| 12 | 5638956 |
| 13 | 21290368 |
| 14 | 81183858 |
| 15 | 312262954 |
| 16 | 1210023672 |
| 17 | 4718194516 |
| 18 | 18492663102 |
| 19 | 72787129726 |
| 20 | 287468548548 |
| 21 | 1138446338344 |
| 22 | 4518338475786 |
| 23 | 17963524388818 |
| 24 | 71514144464784 |
[4,16,58,204,712,2490,8770,31200,112300,409254, 1510102,5638956,21290368,81183858,312262954, 1210023672,4718194516,18492663102,72787129726, 287468548548,1138446338344,4518338475786, 17963524388818,71514144464784] |