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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 66 |
| 6 | 210 |
| 7 | 658 |
| 8 | 2036 |
| 9 | 6236 |
| 10 | 18928 |
| 11 | 57032 |
| 12 | 170790 |
| 13 | 508748 |
| 14 | 1508462 |
| 15 | 4454576 |
| 16 | 13107640 |
| 17 | 38446722 |
| 18 | 112448726 |
| 19 | 328044512 |
| 20 | 954771282 |
| 21 | 2772970950 |
| 22 | 8038036642 |
| 23 | 23258558892 |
| 24 | 67190053760 |
| 25 | 193807573324 |
| 26 | 558249440024 |
| 27 | 1605908314802 |
[0,2,6,20,66,210,658,2036,6236,18928,57032,170790, 508748,1508462,4454576,13107640,38446722, 112448726,328044512,954771282,2772970950, 8038036642,23258558892,67190053760,193807573324, 558249440024,1605908314802] |