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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 19 |
| 4 | 69 |
| 5 | 258 |
| 6 | 1009 |
| 7 | 4051 |
| 8 | 16620 |
| 9 | 69339 |
| 10 | 293485 |
| 11 | 1255837 |
| 12 | 5427580 |
| 13 | 23650266 |
| 14 | 103780197 |
| 15 | 458260421 |
| 16 | 2034519989 |
| 17 | 9075959960 |
| 18 | 40663040317 |
| 19 | 182882049074 |
| 20 | 825372922736 |
| 21 | 3736795149850 |
| 22 | 16966383950246 |
| 23 | 77235724826460 |
| 24 | 352445379796634 |
| 25 | 1611854862549043 |
| 26 | 7386683542925906 |
| 27 | 33915357128568520 |
[1,2,6,19,69,258,1009,4051,16620,69339,293485, 1255837,5427580,23650266,103780197,458260421, 2034519989,9075959960,40663040317,182882049074, 825372922736,3736795149850,16966383950246, 77235724826460,352445379796634,1611854862549043, 7386683542925906,33915357128568520] |