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A018211 as a simple table
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 20 |
| 3 | 60 |
| 4 | 170 |
| 5 | 396 |
| 6 | 868 |
| 7 | 1716 |
| 8 | 3235 |
| 9 | 5720 |
| 10 | 9752 |
| 11 | 15912 |
| 12 | 25236 |
| 13 | 38760 |
| 14 | 58200 |
| 15 | 85272 |
| 16 | 122661 |
| 17 | 173052 |
| 18 | 240460 |
| 19 | 328900 |
| 20 | 444158 |
| 21 | 592020 |
| 22 | 780572 |
| 23 | 1017900 |
| 24 | 1315015 |
| 25 | 1682928 |
| 26 | 2136304 |
| 27 | 2689808 |
| 28 | 3362600 |
| 29 | 4173840 |
| 30 | 5148144 |
| 31 | 6310128 |
[1,4,20,60,170,396,868,1716,3235,5720,9752,15912, 25236,38760,58200,85272,122661,173052,240460, 328900,444158,592020,780572,1017900,1315015, 1682928,2136304,2689808,3362600,4173840,5148144, 6310128] |