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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 32 |
| 3 | 220 |
| 4 | 1498 |
| 5 | 10243 |
| 6 | 70037 |
| 7 | 478941 |
| 8 | 3275421 |
| 9 | 22400407 |
| 10 | 153196114 |
| 11 | 1047708300 |
| 12 | 7165282183 |
| 13 | 49003412145 |
| 14 | 335134684958 |
| 15 | 2291988565129 |
| 16 | 15674926737950 |
| 17 | 107200940180870 |
| 18 | 733148025596363 |
| 19 | 5014004790884386 |
| 20 | 34290816000118746 |
[4,32,220,1498,10243,70037,478941,3275421, 22400407,153196114,1047708300,7165282183, 49003412145,335134684958,2291988565129, 15674926737950,107200940180870,733148025596363, 5014004790884386,34290816000118746] |