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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 72 |
| 5 | 278 |
| 6 | 1115 |
| 7 | 4621 |
| 8 | 19636 |
| 9 | 84959 |
| 10 | 373712 |
| 11 | 1664116 |
| 12 | 7493105 |
| 13 | 34046132 |
| 14 | 155922456 |
| 15 | 718990578 |
| 16 | 3335141541 |
| 17 | 15552372406 |
| 18 | 72859635607 |
| 19 | 342751911710 |
| 20 | 1618370036557 |
| 21 | 7666976762013 |
| 22 | 36431523233690 |
| 23 | 173586679447721 |
| 24 | 829155017445644 |
| 25 | 3969551383992211 |
| 26 | 19043725820723301 |
| 27 | 91536357017160498 |
[1,2,6,20,72,278,1115,4621,19636,84959,373712, 1664116,7493105,34046132,155922456,718990578, 3335141541,15552372406,72859635607,342751911710, 1618370036557,7666976762013,36431523233690, 173586679447721,829155017445644,3969551383992211, 19043725820723301,91536357017160498] |