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| n | a(n) |
|---|---|
| 0 | 4 |
| 1 | 12 |
| 2 | 52 |
| 3 | 275 |
| 4 | 1539 |
| 5 | 8883 |
| 6 | 51974 |
| 7 | 306464 |
| 8 | 1815791 |
| 9 | 10791313 |
| 10 | 64266028 |
| 11 | 383289080 |
| 12 | 2288430270 |
| 13 | 13674181949 |
| 14 | 81759268145 |
| 15 | 489087871679 |
| 16 | 2926904894187 |
| 17 | 17521456528700 |
| 18 | 104917324472297 |
| 19 | 628377368081285 |
| 20 | 3764220848092978 |
| 21 | 22552713068921032 |
| 22 | 135139349515525416 |
[4,12,52,275,1539,8883,51974,306464,1815791, 10791313,64266028,383289080,2288430270, 13674181949,81759268145,489087871679, 2926904894187,17521456528700,104917324472297, 628377368081285,3764220848092978, 22552713068921032,135139349515525416] |