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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 22 |
| 3 | 118 |
| 4 | 646 |
| 5 | 3602 |
| 6 | 20358 |
| 7 | 116272 |
| 8 | 669516 |
| 9 | 3880216 |
| 10 | 22605350 |
| 11 | 132252980 |
| 12 | 776446672 |
| 13 | 4571648804 |
| 14 | 26982643512 |
| 15 | 156306697586 |
| 16 | 918491822736 |
| 17 | 5419056033902 |
| 18 | 32057939582902 |
| 19 | 190020627554666 |
| 20 | 1111060374626770 |
[4,22,118,646,3602,20358,116272,669516,3880216, 22605350,132252980,776446672,4571648804, 26982643512,156306697586,918491822736, 5419056033902,32057939582902,190020627554666, 1111060374626770] |