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| n | a(n) |
|---|---|
| 1 | 6 |
| 2 | 30 |
| 3 | 156 |
| 4 | 810 |
| 5 | 4106 |
| 6 | 21132 |
| 7 | 108124 |
| 8 | 553828 |
| 9 | 2837376 |
| 10 | 14532678 |
| 11 | 74442728 |
| 12 | 381318484 |
| 13 | 1953232394 |
| 14 | 10005076766 |
| 15 | 51249191766 |
| 16 | 262514541710 |
| 17 | 1344682852464 |
| 18 | 6887891796282 |
| 19 | 35281965360630 |
| 20 | 180725414294348 |
| 21 | 925732869184032 |
[6,30,156,810,4106,21132,108124,553828,2837376, 14532678,74442728,381318484,1953232394, 10005076766,51249191766,262514541710, 1344682852464,6887891796282,35281965360630, 180725414294348,925732869184032] |