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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 4 |
| 2 | 18 |
| 3 | 38 |
| 4 | 108 |
| 5 | 274 |
| 6 | 726 |
| 7 | 1892 |
| 8 | 4962 |
| 9 | 12982 |
| 10 | 33996 |
| 11 | 88994 |
| 12 | 232998 |
| 13 | 609988 |
| 14 | 1596978 |
| 15 | 4180934 |
| 16 | 10945836 |
| 17 | 28656562 |
| 18 | 75023862 |
| 19 | 196415012 |
| 20 | 514221186 |
| 21 | 1346248534 |
| 22 | 3524524428 |
| 23 | 9227324738 |
| 24 | 24157449798 |
| 25 | 63245024644 |
| 26 | 165577624146 |
| 27 | 433487847782 |
[0,4,18,38,108,274,726,1892,4962,12982,33996, 88994,232998,609988,1596978,4180934,10945836, 28656562,75023862,196415012,514221186,1346248534, 3524524428,9227324738,24157449798,63245024644, 165577624146,433487847782] |