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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 8 |
| 4 | 20 |
| 5 | 56 |
| 6 | 180 |
| 7 | 596 |
| 8 | 2068 |
| 9 | 7316 |
| 10 | 26272 |
| 11 | 95420 |
| 12 | 349716 |
| 13 | 1290872 |
| 14 | 4794088 |
| 15 | 17896832 |
| 16 | 67110932 |
| 17 | 252648992 |
| 18 | 954444608 |
| 19 | 3616828364 |
| 20 | 13743921632 |
| 21 | 52357746896 |
| 22 | 199911300472 |
| 23 | 764877836468 |
| 24 | 2932031358484 |
| 25 | 11258999739560 |
| 26 | 43303843861744 |
| 27 | 166799988689300 |
[1,2,4,8,20,56,180,596,2068,7316,26272,95420, 349716,1290872,4794088,17896832,67110932, 252648992,954444608,3616828364,13743921632, 52357746896,199911300472,764877836468, 2932031358484,11258999739560,43303843861744, 166799988689300] |