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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 16 |
| 3 | 60 |
| 4 | 228 |
| 5 | 852 |
| 6 | 3180 |
| 7 | 11796 |
| 8 | 43644 |
| 9 | 160980 |
| 10 | 592572 |
| 11 | 2177268 |
| 12 | 7988700 |
| 13 | 29277204 |
| 14 | 107195196 |
| 15 | 392179380 |
| 16 | 1433907228 |
| 17 | 5240022612 |
| 18 | 19140884220 |
| 19 | 69894090996 |
| 20 | 255150047964 |
| 21 | 931214323860 |
| 22 | 3397977981372 |
| 23 | 12397189043508 |
| 24 | 45224087388060 |
[4,16,60,228,852,3180,11796,43644,160980,592572, 2177268,7988700,29277204,107195196,392179380, 1433907228,5240022612,19140884220,69894090996, 255150047964,931214323860,3397977981372, 12397189043508,45224087388060] |