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 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | -18 |
| 4 | -240 |
| 5 | 1900 |
| 6 | 42372 |
| 7 | -482552 |
| 8 | -14970816 |
| 9 | 222612624 |
| 10 | 8825080100 |
| 11 | -161981127968 |
| 12 | -7809130867824 |
| 13 | 170561613679808 |
| 14 | 9678967816041188 |
| 15 | -245159013138710400 |
| 16 | -16000787866533953280 |
| 17 | 461102348510408544512 |
| 18 | 34017524842099233036996 |
| 19 | -1098983344602124698522112 |
| 20 | -90417110945911655996319600 |