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 | 1 |
| 3 | -1 |
| 4 | 2 |
| 5 | 6 |
| 6 | -264 |
| 7 | 5370 |
| 8 | -93750 |
| 9 | 1315706 |
| 10 | -3543736 |
| 11 | -880688376 |
| 12 | 56549341380 |
| 13 | -2612825765748 |
| 14 | 99009763750128 |
| 15 | -2593891139126560 |
| 16 | -31860555469490020 |
| 17 | 12585468136754891100 |
| 18 | -1364794494618494224128 |
| 19 | 114095029934565534862680 |
| 20 | -7984695190944325311086112 |
| 21 | 419424013080533747232201968 |