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 | 1 |
| 2 | 0 |
| 3 | -4 |
| 4 | 14 |
| 5 | -18 |
| 6 | -168 |
| 7 | 1920 |
| 8 | -11898 |
| 9 | 27398 |
| 10 | 582896 |
| 11 | -13028904 |
| 12 | 183020620 |
| 13 | -2061910004 |
| 14 | 17930433744 |
| 15 | -65293856160 |
| 16 | -1965585556410 |
| 17 | 69343044999750 |
| 18 | -1519055329884960 |
| 19 | 26755366818127560 |
| 20 | -374375460816570780 |
| 21 | 2924763867241325220 |