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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 19 |
| 4 | 68 |
| 5 | 255 |
| 6 | 984 |
| 7 | 3929 |
| 8 | 16013 |
| 9 | 66253 |
| 10 | 278482 |
| 11 | 1183947 |
| 12 | 5079517 |
| 13 | 21992997 |
| 14 | 95913334 |
| 15 | 420824859 |
| 16 | 1857477019 |
| 17 | 8239560040 |
| 18 | 36707294405 |
| 19 | 164224110552 |
| 20 | 737390796048 |
| 21 | 3321642113284 |
| 22 | 15009789841105 |
| 23 | 68013861083631 |
| 24 | 308958608029480 |
| 25 | 1406890127444539 |
| 26 | 6420448495277942 |
| 27 | 29358341405419166 |
[1,2,6,19,68,255,984,3929,16013,66253,278482, 1183947,5079517,21992997,95913334,420824859, 1857477019,8239560040,36707294405,164224110552, 737390796048,3321642113284,15009789841105, 68013861083631,308958608029480,1406890127444539, 6420448495277942,29358341405419166] |