This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | -4 |
| 3 | 32 |
| 4 | -240 |
| 5 | 2064 |
| 6 | -18816 |
| 7 | 179264 |
| 8 | -1762816 |
| 9 | 17758976 |
| 10 | -182342400 |
| 11 | 1901196288 |
| 12 | -20075427840 |
| 13 | 214246524928 |
| 14 | -2307200135168 |
| 15 | 25039992254464 |
| 16 | -273603550461952 |
| 17 | 3007387399258112 |
| 18 | -33230774508716032 |
| 19 | 368915340555517952 |
| 20 | -4112806343370539008 |