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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 28 |
| 5 | 255 |
| 6 | 744 |
| 7 | 2418 |
| 8 | 20440 |
| 9 | 65535 |
| 10 | 548856 |
| 11 | 2835756 |
| 12 | 4059264 |
| 13 | 4451832 |
| 14 | 10890040 |
| 15 | 13192608 |
| 16 | 23001132 |
| 17 | 54949482 |
| 18 | 110771178 |
| 19 | 220174080 |
| 20 | 445701354 |
| 21 | 4294967295 |
| 22 | 16331433888 |
| 23 | 18377794080 |
| 24 | 94951936080 |
| 25 | 204721968000 |
| 26 | 386940247200 |
| 27 | 601662398400 |
| 28 | 1433565580920 |
[1,3,15,28,255,744,2418,20440,65535,548856, 2835756,4059264,4451832,10890040,13192608, 23001132,54949482,110771178,220174080,445701354, 4294967295,16331433888,18377794080,94951936080, 204721968000,386940247200,601662398400, 1433565580920] |