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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 8 |
| 4 | 50 |
| 5 | 424 |
| 6 | 4472 |
| 7 | 55760 |
| 8 | 797022 |
| 9 | 12801296 |
| 10 | 227829866 |
| 11 | 4446822688 |
| 12 | 94422531876 |
| 13 | 2166975912496 |
| 14 | 53457972027254 |
| 15 | 1410960809766320 |
| 16 | 39680975219789210 |
| 17 | 1184783226216138592 |
| 18 | 37434788449030871076 |
| 19 | 1248022160663960432264 |
| 20 | 43785432805297352937954 |
| 21 | 1612690422384099635004264 |
[1,1,2,8,50,424,4472,55760,797022,12801296, 227829866,4446822688,94422531876,2166975912496, 53457972027254,1410960809766320,39680975219789210, 1184783226216138592,37434788449030871076, 1248022160663960432264,43785432805297352937954, 1612690422384099635004264] |