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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 20 |
| 5 | 68 |
| 6 | 196 |
| 7 | 516 |
| 8 | 1284 |
| 9 | 3076 |
| 10 | 7172 |
| 11 | 16388 |
| 12 | 36868 |
| 13 | 81924 |
| 14 | 180228 |
| 15 | 393220 |
| 16 | 851972 |
| 17 | 1835012 |
| 18 | 3932164 |
| 19 | 8388612 |
| 20 | 17825796 |
| 21 | 37748740 |
| 22 | 79691780 |
| 23 | 167772164 |
| 24 | 352321540 |
| 25 | 738197508 |
| 26 | 1543503876 |
| 27 | 3221225476 |
| 28 | 6710886404 |
| 29 | 13958643716 |
| 30 | 28991029252 |
| 31 | 60129542148 |
[0,0,4,20,68,196,516,1284,3076,7172,16388,36868, 81924,180228,393220,851972,1835012,3932164, 8388612,17825796,37748740,79691780,167772164, 352321540,738197508,1543503876,3221225476, 6710886404,13958643716,28991029252,60129542148] |