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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 72 |
| 5 | 262 |
| 6 | 986 |
| 7 | 3732 |
| 8 | 14308 |
| 9 | 55280 |
| 10 | 214610 |
| 11 | 837858 |
| 12 | 3281386 |
| 13 | 12889822 |
| 14 | 50761728 |
| 15 | 200279230 |
| 16 | 791619506 |
| 17 | 3133268528 |
| 18 | 12416918448 |
| 19 | 49259337824 |
| 20 | 195589455772 |
| 21 | 777223955192 |
| 22 | 3090583797818 |
| 23 | 12296847146286 |
| 24 | 48952531584772 |
| 25 | 194965289636094 |
| 26 | 776814154823044 |
| 27 | 3096239527352566 |
[1,2,6,20,72,262,986,3732,14308,55280,214610, 837858,3281386,12889822,50761728,200279230, 791619506,3133268528,12416918448,49259337824, 195589455772,777223955192,3090583797818, 12296847146286,48952531584772,194965289636094, 776814154823044,3096239527352566] |