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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 6 |
| 3 | 14 |
| 4 | 28 |
| 5 | 56 |
| 6 | 150 |
| 7 | 360 |
| 8 | 828 |
| 9 | 1906 |
| 10 | 4628 |
| 11 | 10972 |
| 12 | 25850 |
| 13 | 60948 |
| 14 | 145152 |
| 15 | 343870 |
| 16 | 814072 |
| 17 | 1927632 |
| 18 | 4573086 |
| 19 | 10836712 |
| 20 | 25678860 |
| 21 | 60851842 |
| 22 | 144253956 |
| 23 | 341881772 |
| 24 | 810275098 |
| 25 | 1920403380 |
| 26 | 4551789280 |
| 27 | 10788216718 |
| 28 | 25569422984 |
| 29 | 60602792000 |
[4,6,14,28,56,150,360,828,1906,4628,10972,25850, 60948,145152,343870,814072,1927632,4573086, 10836712,25678860,60851842,144253956,341881772, 810275098,1920403380,4551789280,10788216718, 25569422984,60602792000] |