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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 30 |
| 3 | 180 |
| 4 | 1078 |
| 5 | 6468 |
| 6 | 38808 |
| 7 | 232845 |
| 8 | 1397067 |
| 9 | 8382394 |
| 10 | 50294353 |
| 11 | 301766110 |
| 12 | 1810596649 |
| 13 | 10863579883 |
| 14 | 65181479283 |
| 15 | 391088875684 |
| 16 | 2346533254087 |
| 17 | 14079199524505 |
| 18 | 84475197147008 |
| 19 | 506851182882025 |
| 20 | 3041107097292125 |
| 21 | 18246642583752723 |
| 22 | 109479855502516309 |
| 23 | 656879133015097824 |
[4,30,180,1078,6468,38808,232845,1397067,8382394, 50294353,301766110,1810596649,10863579883, 65181479283,391088875684,2346533254087, 14079199524505,84475197147008,506851182882025, 3041107097292125,18246642583752723, 109479855502516309,656879133015097824] |