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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 56 |
| 4 | 176 |
| 5 | 520 |
| 6 | 1456 |
| 7 | 3896 |
| 8 | 10048 |
| 9 | 25100 |
| 10 | 60960 |
| 11 | 144440 |
| 12 | 334752 |
| 13 | 760456 |
| 14 | 1696464 |
| 15 | 3722224 |
| 16 | 8043040 |
| 17 | 17135624 |
| 18 | 36031104 |
| 19 | 74840568 |
| 20 | 153680928 |
| 21 | 312198160 |
| 22 | 627828272 |
| 23 | 1250540024 |
| 24 | 2468443296 |
| 25 | 4830809868 |
| 26 | 9377190336 |
| 27 | 18061370288 |
| 28 | 34531009760 |
| 29 | 65552873736 |
[1,4,16,56,176,520,1456,3896,10048,25100,60960, 144440,334752,760456,1696464,3722224,8043040, 17135624,36031104,74840568,153680928,312198160, 627828272,1250540024,2468443296,4830809868, 9377190336,18061370288,34531009760,65552873736] |