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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 10 |
| 3 | 24 |
| 4 | 208 |
| 5 | 700 |
| 6 | 8230 |
| 7 | 29144 |
| 8 | 381304 |
| 9 | 19175140 |
| 10 | 71582944 |
| 11 | 3817763740 |
| 12 | 54975633976 |
| 13 | 209430787824 |
| 14 | 3059510616424 |
| 15 | 173215372864600 |
| 16 | 9938978487990064 |
| 17 | 38430716856090160 |
| 18 | 2235968978631715024 |
| 19 | 33731189163354610720 |
| 20 | 131176846748288854980 |
| 21 | 7749524484709164817824 |
[4,10,24,208,700,8230,29144,381304,19175140, 71582944,3817763740,54975633976,209430787824, 3059510616424,173215372864600,9938978487990064, 38430716856090160,2235968978631715024, 33731189163354610720,131176846748288854980, 7749524484709164817824] |