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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 12 |
| 3 | 56 |
| 4 | 240 |
| 5 | 994 |
| 6 | 4032 |
| 7 | 16280 |
| 8 | 65280 |
| 9 | 261626 |
| 10 | 1047552 |
| 11 | 4192266 |
| 12 | 16773160 |
| 13 | 67100670 |
| 14 | 268419048 |
| 15 | 1073709056 |
| 16 | 4294901774 |
| 17 | 17179738108 |
| 18 | 68719214620 |
| 19 | 274877382642 |
| 20 | 1099510579208 |
| 21 | 4398044413950 |
| 22 | 17592181850104 |
| 23 | 70368735789062 |
| 24 | 281474959933418 |
| 25 | 1125899873288212 |
[0,2,12,56,240,994,4032,16280,65280,261626, 1047552,4192266,16773160,67100670,268419048, 1073709056,4294901774,17179738108,68719214620, 274877382642,1099510579208,4398044413950, 17592181850104,70368735789062,281474959933418, 1125899873288212] |